/\. 


rrA- 


The  Mechanics 
0/ Fitting  Glasses 


By 
Robert  D.  Pettet 


Giving  complete  information  concerning 
fitting,  adjusting  and  prescribing  eyeglass 
and  spectacle  frames  and  mountings,  and 
covering  all  mechanical  work  within  the 
province  of  the  refractionist. 


PUBLISHED     BY 

TOPAZ    &     KAEMERLE 

CHICAGO 


OPTOMETRy 


Copyright 
1913 


Introduction 


THE  purpose  of  thi^  book  is  to  impart  to  the  refrac- 
tionist  information  regarding  the  mechanical  side 
of  fitting  glasses,  principally  the  adjustment  and 
fitting  of  eyeglass  and  spectacle  frames  and  mountings. 
It  is  designed  to  meet  the  great  demand  for  data  of  this 
kind  presented  in  a  practical  way  and  which  are  omitted 
from  text  books  on  refraction.  The  descriptions  and  in- 
structions are  confined  to  modern  types  of  eyeglasses  and 
spectacles,  and  antique  styles  are  not  discussed  except 
where  they  have  some  bearing  on  present  day  fitting. 

The  book  has  for  its  foundation  the  extended  prac- 
tical experience  of  the  author  and  observation  of  the 
methods  of  others  that  have  come  to  his  attention. 


Table  of  Subjects 


Definitions  and  illnstrations  of  different  styles  and  parts 

of  eyeglasses,  spectacles  and  lenses. 
Inset  and  Outset  studs  explained. 
Miscellaneous   frames   and   mountings   described, 
Miscellaneous  lenses  described. 
How  to  ascei'tain  the  correct  frame  or  mounting. 
Measuring  the  pupillary  distance,  only  one  correct  way. 
Measuring  for  and  the  fitting  of  spectacles. 
Measuring  for  and  the  fitting  of  eyeglasses. 
How   to    fit    frames    and    mountings   containing   l)ifocal 

lenses. 
How  to  adjust  spectacles. 
How  to  adjust  eyeglasses. 
Kinds  of  pliers  to  use. 

How  to  judge  a  good  fingerpiece  eyeglass  mounting. 
How  to  write  prescriptions. 
Drilling  of  holes  in  lenses. 
Ascertaining  the  power  of  lenses. 
How  to   ascertain  the  position   of  the  plus   and   minus 

cylinder  in  compound  lenses  l)y  simple  inspection. 
How  to  construct  a  chart  to  measure  prisms  and  to  detect 

a  prism  i^ower  in  lenses. 
Transpositions  simplified. 
How  to  de-center  lenses  to  obtain  definite  prism  powers, 

formulas,  etc. 
How  to  mount  rimless  lenses. 
What  to  do  for  loose  screws. 
Record  systems. 


Definitions 


Frames :  Fixtures  that  have  rims  going  around  the 
lenses. 

Mountings :    Fixtures  that  hold  rimless  lenses. 

Speetaeles:  Fixtures  that  are  held  in  position  by 
means  of  bows  (temples)  that  go  around  the  side  of  the 
head  and  by  a  bi-idge  that  rests  on  the  crown  of  tlie  nose. 
When  these  have  rims  aromid  the  lenses  they  are  known 
as  spectacle  frames  and  when  there  are  no  rims  around 
the  lenses  they  are  known  as  spectacle  mountings. 

Eyeglasses:  Fixtures  that  are  held  in  position  on 
the  nose  by  springs  and  l)y  guards  that  press  on  the  sides 
of  the  nose.  With  rims  around  the  lenses  they  are  eye- 
glass frames  and  without  rims  they  are  eyeglass 
mountings. 

Spectacles 

Temples:  Attachments  on  spectacles  that  go  around 
the  side  of  the  face  and  over  the  ears.  Straight  temples 
go  straight  back  and  do  not  circle  the  ears.  Riding 
temples  (sometimes  called  riding  bows)  go  entirely 
around  the  back  of  the  ears.  Half-riding  temples  are  half 
way  between  the  straight  temple  and  riding  temple  vari- 
eties, just  turning  slightly  over  the  back  of  the  ears. 

Regular  Temples :    The  ordinary  wire  temples. 

Cable  Temples:  Made  by  wrapping  two  pieces  of 
pliable  wire  about  each  other. 

Half-Cable  Temples:  The  part  from  the  frame  to 
the  top  of  the  ear  is  of  the  regular  stiff  wire,  the  part 

9 


10 


THE      MECHANICS      OF      FITTING      GLASSES 


Spectacle    Mounting. 

going  aruuiul  the  cars  is  cable.  There  are  several  vari- 
eties of  this  kind:  C'onifort  Temples,  Apex  Temples, 
Velvet  End  Temples,  etc.;  these  are  very  similar  in  con- 
strnetion  and  ditfer  only  in  the  manner  in  which  the  soft 
j)ortion  that  encircles  the  ear  is  attached  to  the  wire  that 
goes  to  the  frame.  They  are  all  very  soft  and  pliable  on 
the  ear  end  and  are  intended  to  increase  the  amount  of 


Spectacle    Frame. 


comfort  and  eliminate  the  features  of  the  regular  wire 
temples  that  tend  to  make  the  latter  uncomfortable  about 
the  ear. 

Bridge:  The  part  of  a  spectacle  that  rests  on  the 
nose  and  connects  the  two  lenses.  This  is  the  central  and 
most  important  portion  of  a  spectacle. 

Shanks :  The  ends  of  the  bridge  that  point  outward 
from  the  nose  and  connect  with  the  lenses. 

Straps:  The  attachments  at  the  end  of  the  shanks 
and  tem})]es  on  rimless  ^nounliiigs  by  means  of  which  the 
lenses  are  held  to  the  mounting. 


THE      MECHANICS      OF      FITTING      Cxi.ASSES 


11 


End-pieces:  The  parts  to  which  the  temples  are  at- 
tached in  rimless  mountings;  they  include  the  straps 
which  are  really  a  part  of  them.  When  spoken  of  in  con- 
nection with  temples  they  are  familiarly  known  as 
"ends,"  for  instance,  we  speak  of  "temples  and  ends." 

Eye-wires:  The  rims  that  encircle  the  lenses  on 
frames. 


Eyeglasses   (Regular) , 


Eyeglass    Mounting. 


Eyeglass    Frame. 


Spring:  The  central  part  of  the  frame  or  mounting 
corresponding  to  the  In-idge  of  spectacles.  There  are  sev- 
eral styles  of  springs  as  shown  l)y  the  illustrations  given 
here.  In  addition  to  the  dit¥erent  varieties  there  are  dif- 
ferent sizes;  the  usual  length  of  the  oblong  style  is  21/8 
inches,  and  of  the  hoop  style  2  inches.  Oblong  springs  are 
sometimes  called  "square"  springs  and  hoop  springs  are 
sometimes  called  "oval." 


u 


F"ull.         Reduced. 


GRECIAN 


Tilting. 


Adjustable, 


12 


THE      MECHANICS      OF      FITTIXC;      Gf. ASSES 


Guards:  Tlie  parts  that  lie  against  the  side  of  the 
nose  and  hold  to  the  flesh;  often  called  by  the  laity 
"elips."  By  consult ing  catalogs  of  the  wholesale  optical 
houses  it  will  be  seen  that  there  are  countless  styles  and 
designs.    A  few  of  the  most  common  are  shown  here. 


^ 


Wells. 


Anchor. 


Schwab.       Anatomical.     Bausch.       Solid. 


Studs:  The  parts  that  hold  the  lenses  to  the  mount- 
ing and  which  join  the  guards  and  the  spring. 

Open  Studs:  Those  in  which  the  nasal  side  of  the 
studs  is  left  open. 

Box  Studs :  In  these  the  portion  into  which  the 
guard  and  spring  fit  is  constructed  like  a  ])ox  and  the 
nasal  side  is  closed,  the  stud-screw  is  countersunk,  and 
thus  tliere  are  no  rough  parts  or  exposed  screws  in  con- 
tact with  the  flesh. 

In  addition  to  these  two  styles  there  are  many  sizes, 
that  is,  some  have  longer  posts  than  others,  the  purpose 
of  which  is  to  regulate  the  distance  between  the  lenses. 
There  are  also  ''drop"  studs  to  lower  the  lenses;  these 
are  made  in  two  sizes — 1-1(5  i\\n\  1-8  inch. 


ABODE 

From   tlic   illiisti-ation    it    will   be  observed  that  the 
sizes  of  studs  (controlled  by  the  length  of  the  post)  are 


THE      MECHANICS      OF      FITTIXG      GLASSES  13 

indicated  by  the  letters  A,  B,  L\  D,  E,  and  F ;  A  l)eing  the 
shortest  and  F  the  longest,  with  about  one  niillinieter  be- 
tween each  succeeding  size. 

Inset  and  Outset  Studs:  Confusion  exists  in  tlie 
mind  of  every  beginner  in  the  matter  of  inset  and  outset 
studs,  and  it  must  be  admitted  that  there  is  good  reason 
for  this,  and  the  beginner  cannot  l)e  criticized  for  any 
misunderstandings  he  may  have  in  this  regard,  for  the 
fact  is  there  is  so  much  difference  of  opinion  in  the  minds 
of  various  opticians  and  wholesale  houses  that  it  is  never 
safe  to  specify  "inset"  or  "outset"  until  you  know  what 
the  person  or  house  to  whom  you  are  writing  means  by 
these  terms.  Most  whok^sale  catalogs  state  that  inset 
studs  set  the  lenses  farther  from  the  eyes  and  that  outset 
studs  set  the  lenses  closer  to  the  eyes.  To  the  mind  of  the 
average  man  who  has  not  become  accustomed  to  this 
translation  of  the  terms  they  will  seem  to  be  reversed. 
Where  this  usage  of  the  terms  originated  was  with  the 
idea  that  inset  studs  set  the  mounting  in  toward  the  face 
and  consequently  the  lenses  were  set  farther  from  the 
eyes,  however  when  we  realize  that  the  mounting  always 
stays  in  the  same  position  on  the  nose  and  it  is  the  lenses 
themselves  that  are  moved  it  would  most  certainly  seem 
that  studs  that  set  the  lenses  out  should  be  termed  "out- 
set," but  the  term  is  not  generally  accepted  this  way,  so 
that  the  safest  plan  in  writing  prescriptions,  etc.,  that  you 
are  sending  away  to  be  filled  is  always  to  say  "to  set  the 
lenses  closer  to  the  eyes"  or  "farther  away,"  as  may  be 
wanted,  for  instance:  "Inset  studs,  to  set  the  lenses 
farther  from  the  eyes"  or  whatever  way  you  want  to  put 
it,  so  that  what  you  want  will  be  clearly  understood. 


14  THE      MECHANICS      OF      FITTING      GLASSES 

Eyeglasses   (Finger-Piece). 


Bridge:  Same  as  the  bridge  in  spectacles.  This 
usually  includes  the  studs,  as  they  are  generally  made  in 
one  piece. 

Finger-pieces :  The  projecting  ends  in  front  that  are 
grasped  by  the  tips  of  the  fingers  in  order  to  operate  the 
spreading  of  the  guards. 

Springs:  These  connect  directly  with  the  guards 
and  cause  them  to  press  inward  toward  the  nose. 

Finger-i^iece  eyeglasses  are  made  in  a  great  number 
of  styles  and  combinations  and  are  given  particular  names 
by  the  various  manufacturers.  While  eyeglasses  of  this 
design  appear  at  first  sight  to  be  very  much  alike,  closer 
inspection  and  study  will  show  that  there  are  several 
classifications.  This  subject  is  discussed  in  another  por- 
tion of  this  book  under  the  heading  ''How  to  Judge  a 
Good  Finger-piece  Eyeglass  ]\rounting. " 

Miscellaneous  Frames  and  Mountings. 
Grab  fronts  are  fixtures  to  contain  lenses,  usually  the 
addition  for  reading,  whicli  attach  to  the  outside  of  spec- 


tacles, and  may  be  taken  off  and  ]uit  on  without  removing 
the  spectacles  proi)er.     Grab  fronts  may  be  either  with 


THE      MECHANICS      (3F      FITTING      GI.ASSES 


15 


rims  or  rimless.  Grab  l)acks  arc  similar  to  grab  fronts 
except  that  they  attach  to  the  back  of  the  spectacles  in- 
stead of  the  front. 

Specalettes  are  a  combination    of    eyeglasses    and 
spectacles,  that  is  they  are  eyeglasses  with  temples.  These 


are  desirable  where  the  patient  has  a  straight  and  nearly 
vertical  nose  and  experiences  difficnlty  in  retaining  a 
spectacle  bridge  in  the  proper  position  and  in  cases  where 
the  skin  on  the  front  of  the  nose  is  very  sensitive.    There 


are  several  forms  of  these  monntings  and  catalogs  of 
wholesale  optical  houses  should  be  consulted  on  the 
matter. 


General  Description  of  Dif- 
ferent Kinds  of  Lenses. 


It  is  thought  that  the  simple  forms,  like  double  con- 
cave and  convex  and  periscopic  concave  and  convex,  are 
so  well  known  and  understood  they  need  no  explanation, 
so  we  shall  proceed  at  once  to  the  more  advanced  types. 

Toric :  A  lens  having  three  curves.  It  has  the  ap- 
pearance of  a  very  deep  periscopic,  having  one  side  deep 
convex  and  the  other  deep  concave.  By  reason  of  its  defi- 
nition a  toric  lens  can  never  be  a  sphere,  but  is  always 
either  a  cylinder  or  sphero-cylinder.  Tories  are  built  on 
three  base  curves — the  3,  6  and  9  D. 

Meniscus :  A  lens  built  on  the  deep  periscopic  form. 
This  kind  of  lens  is  always  a  sphere  and  is  often,  though 
incorrectly,  called  a  "spherical  toric."  This  latter  term 
has  come  into  such  common  use  that  it  is  generally  ac- 
cepted without  question,  in  fact  there  are  many  in  the 
business  who  do  not  know  that  the  term  is  technically 
wrong. 

Bifocals:  Any  lenses  that  are  composed  of  two 
parts  or  have  two  foci.  Usually  these  lenses  combine 
the  distant  and  near  correction,  the  upper  part  for  dis- 
tance and  the  lower  for  reading. 

16 


THE      MECHAXirS      OF      FITTING      GLASSES 


17 


Cement  Bifocals:  Any  Infoeal  lenses  in  which  the 
reading  or  near  correction  segments  are  attached  to  the 
main  lens  by  cement,  bnt  nsnally  understood  to  mean 
bifocals  where  the  segments  (or  scales)  are  not  especially 
thin  and  which  are  elliptical  in  shape. 

Opifex  Bifocals:  Lenses  in  which  the  reading  seg- 
ments are  very  thin,  usually  round,  and  attached  to  the 
main  lens  by  cement.  Sometimes  called  "semi-invisible" 
bifocals. 

Kryptok  Bifocals:  Lenses  in  which  the  reading  seg- 
ments are  practically  invisible  and  in  which  the  segment 
is  fused  to  the  main  lens  forming  one  piece  of  glass.  The 
segment  and  main  lens  are  of  different  indices  of  refrac- 
tion. There  are  other  makes  of  fused  bifocals,  but  the 
Kryptok  is  the  most  widely  known  and  used. 

Perfection  Bifocals:  Lenses  composed  of  two  sep- 
arate pieces  of  glass  held  in  position  by  the  rims  of  the 
frames. 


18 


THE      MPX'HANICS      OF      FITTING      GLASSES 


LentioTilars:  Lenses  of  n  iiiiims  power  in  which  the 
peripheral  i^ortions  have  been  gronnd  off  flat  or  to  a 
convex  edge  for  the  pnrpose  of  lightening  the  weight  of 

the  lenses  and  m.-ddng  them  thinner  on  tlie  edges. 


Ova!  1.1  nil 


Round  Lenticular 


Colored  Lenses:  There  are  many  different  kinds 
and  colors  used,  the  prime  pnrpose  being  to  reduce  the 
amount  of  light  that  enters  the  eye.  Smoked  lenses  are 
made  in  varying  shades  and  densities.  There  are  also 
green  and  blue  lenses.  Much  has  been  claimed  recently 
for  amber  lenses  with  the  idea  that  they  reduce  the  num- 
ber of  ultra  violet  rays  entering  the  eye.  Likewise  claims 
have  been  made  for  pink  and  amethyst  shades.  There 
are  also  lenses  known  by  special  trade  names  most  of 
which  are  a  combination  of  light  green  and  light  amber. 


TABLE    OF    SIZES   OF    LENSES, 


Eye 

Inserts. 

Rimless. 

Short  Oval 

E.ve. 

Inserts. 

mm 

mm 

Rimless. 

mm 

Jumbo 

4fi    x38 

46    x3S 

44.. 5x39. r. 

2 

35x25.5 

(1000 

■H.3x3(! 

44    x36 

42.5x37.5 

3 

34x25 

000 

40.9x.31. 9 

41    x32 

39.5x33.5 

4 

33x24 

00 

39.7x30.7 

40    x31 

38.3x32.5 

A 

39x25 

0 

37.Sx28.S 

3S.5x29.5 

37    x31 

B 

40x26 

1 

30.5x27.5 

37    x28 

35.5x29.5 

C 

37x21 

Shapes  of  Lenses. 


In  the  iiiajoi'ity  of  cases  regular  shape  lenses  should 
be  used,  but  the  short  oval  is  very  advantageous  many 
times.  Where  the  patient  does  a  great  amount  of  near 
work  the  short  oval  offers  a  large  field  of  vision  up  and 
down,  the  direction  in  wliich  it  most  needed.  This  shape 
is  also  desirable  in  cases  of  narrow  P.  I).,  for  here  it  is 
usually  necessary  to  use  small  lenses  which  naturally 
restrict  the  field  of  vision. 

The  leaf  shape  is  designed  for  peo])le  having  heavy 
protruding  brows ;  it  resembles  the  short  oval  with  the 
top  rounded  off.  Odd  shapes  of  lenses — that  is,  any  but 
the  regular  and  short  oval — should  be  generally  avoided, 
for  their  appearance  is  far  from  pleasing  and  gives  a 
suggestion  of  grotes(iueness  to  the  face. 


Regular  Oval. 


Short    Oval. 


Leaf    Shape. 


19 


Ascertaining    the    Correct 
Frame  or  Mounting. 


The  Unit  of  Measure. 

The  English  system  of  lineal  measnres  has  so  long 
been  nsed  in  our  everyday  life  that  it  is  natural  that  this 
system  has  lieen  employed  by  American  opticians  in  giv- 
ing dimensions  of  spectacles,  etc.,  but  since  we  have 
arrived  at  a  place  where  accuracy  and  definiteness  are 
essential,  this  system  is  no  longer  practical.  The  con- 
tinual use  of  fractions  permits  the  occurrence  of  too 
many  errors  and  a  specification  of  1-8  or  1-16  inch  gives 
room  for  too  much  variation  one  way  or  the  other, 
whereas,  if  we  measure  by  the  metric  system  when  dealing 
with  short  distances  we  eliminate  a  large  portion  of  the 
element  of  error  both  in  calculations  and  in  the  matter 
of  personal  equation. 

For  instance,  suppose  we  have  2V8  and  2yo  inches  to 
comjjare.  We  have  a  general  idea  regarding  the  relation 
of  these  two  quantities  and  after  a  little  thought  we 
realize  there  is  a  difference  of  %  inch.  Now  express  the 
same  dimensions  in  millimeters — we  have  53  and  62  milli- 
meters. At  a  glance  we  have  a  definite  appreciation  of 
the  relation  and  know  instantly  that  there  is  a  difference 
of  9  millimeters.  Then  again,  on  a  scale  graduated  in 
millimeters  the  divisions  are  comparatively  close  together 
and  a  slight  variance  around  the  mark  becomes  evident 

20 


THE      MECHANICS      i)V      FITTIXC      GLASSES  21 

at  once.  I'pon  a  iiioint'ut \s  reHectioii  ;iii(l  especially  at"ter 
we  get  deeper  into  this  snbject,  you  will  i-cadily  appreci- 
ate the  advisability  of  nicasni'inii-  in  inillinictcrs  instead 
of  inches. 

Pupillary  Distance. 

There  is  just  one  simple  method  of  ascertaining  the 
exact  distance  between  the  eyes. 

Place  yourself  in  a  position  directly  facing  the  pa- 
tient. Suppose  you  desire  his  P.  D.  for  distance:  Have 
the  patient  look  over  your  head  at  an  object  on  the  wall 
opposite.  Hold  the  rule  in  your  right  hand  in  the  same 
manner  as  you  would  a  pencil  and  steady  your  hand 
by  placing  your  free  fingers  upon  the  side  of  the  patient's 
head.  Now,  with  your  left  eye  (right  eye  closed)  bring 
the  zero  of  the  rule  opposite  the  line  of  demarcation  be- 
tween the  iris  and  sclera,  say,  for  instance  in  this  case, 
on  the  nasal  side  of  the  eye.  Holding  the  rule  in  this  posi- 
tion quickly  open  your  right  eye  and  close  your  left  and 
read  off  the  graduation  mark  opposite  the  edge  of  iris  (in 
this  case  temporal  side)  of  patient's  left  eye.  This  read- 
ing will  give  the  true  width  between  the  eyes.  Of  course 
if  you  measure  from  the  nasal  side  of  one  eye  you  meas- 
ure to  the  temporal  side  of  the  other  eye  and  vice  versa. 

If  you  measure  with  both  your  eyes  open  your  result 
will  vary  2  or  3  millimeters,  because  you  will  not  be  sure 
which  mark  is  opposite  patient's  eye.  If  you  measure  en- 
tirely with  one  eye  the  error  of  parallax  will  enter  so 
much  that  your  readings  will  always  l)e  from  2  to  5  milli- 
meters too  narrow. 

To  prove  the  veracity  of  the  foregoing  statements, 
make  two  marks  about  two  inches  apart  on  a  piece  of 


22 


THE      MECHANICS      OF      FlTTIXCx      Cxi, ASSES 


j)a}»('r;  lay  the  ]);ii)('r  on  your  desk  and  rc'sting  yonr  hand 
on  it  liold  your  rule  one  or  two  inches  above  it.  First 
measure  the  distance  with  both  eyes,  then  measure  it  en- 
tirely with  one  eye,  and  then  with  each  eye  separately 
(the  zero  with  the  left  and  the  total  width  with  the  right 
eye)  and  you  will  find  a  decided  variance  in  your  three 
readings.  By  laying  the  rule  Hat  on  the  paper  and  meas- 
uring the  exact  distance  you  will  find  your  third  measure- 
ment to  be  correct. 

This  cut  shows  the  method  of  measuring  the  i)u- 
pillary  distance,  the  P.  D.  in  this  case  being  55  milli- 
meters, measured  from  the  inside  of  the  right  iris  to  the 
outside  of  the  left. 


P.Z7. 


THE      MECHANICS      OF      FITTING      GLASSES 


23 


The  Spectacle  Bridge. 
There  are  two  ways  of  expressing  the  dimensions  of 
a  bridge:     By  giving  each  dimension  in  figures  or  by 
using    the    size    letter    and    number. 
T  h  e    dimensions     considered     are 
height,    inclination    of    crest,    angle 
and   width   of   base.     The   following 
letters    are    used    to    designate    the 
width  of  bridges,  beginning  with  the 
smallest:  L,  M,  N,  0,  P.   The  heights 
are   expressed   in   combination   with 
the  letters  by  numbers,  as  i/o,  1,  IVo, 
2,  etc.  The  shanks  are  called  regular, 
long  and  extra  long.    With  the  regu- 
lar shanks  the  lenses  are  held  a  trifle 
closer  to  the  eyes  than  the  crest  of 
the    bridge;    with    long    shanks    the 
lenses  and  crest  of  bridge  are  on  the 
same  plane;  with  extra  long  shanks 
the  lenses  are  further  from  the  eyes 
than  the  crest  of  bridge  is.    Thus  to 
set  the  lenses  away  from  the  eyes  to 
escape  the  lashes,  etc.,  we  use  long 
and   extra   long   shanks.     When   no 
length  shank  is  stated  "regular"  is 
understood.      This    is    the    way    the 
different    sizes    of    bridges    are    ex- 
pressed:    M,    Mi/o,    N2    extra    long 
shanks. 

When  the  sizes' are  not  specified 
as  above  it  is  necessary  to  give  all  the 
dimensions  in  figures.    The  height  of 


DIMENSIONS  OF  SAD- 
DLE BRIDGES. 

Upper  figure  Incnes, 
lower  figure  Millimeters). 

Bridge. 
Height. 

w 

a 

n 

L 

0 
0 

0 
0 

5  8 

IS 

I.>2 

V-'i 

0 
0 

15 

LI 

H 
3 

0 
0 

IS 

M 

0 
0 

1.4 

^8 

IS 

5-8 

15 

Ml 

3^ 

Mil  2 

1,4 

15 

M2 

\-4 

6 

fc 

17 

18 

H 
18 

N 

0 
0 

14 

N>4 

!^,. 

t, 

Nl 

1,; 
3 

4'-; 

14 

NIH 

1'^ 

N2 

■i 

,•'4 

18 

20 

•Hi 
2C 

N2y2 

tv. 

3 

N3 

^ 

IH 

0 

0 
0 

0 
0 

>8 

21 
21 

Ol 

3 

IH 

02 

6 

14 

J8 

21 

03 

9 

ti 

.a 

23 

PI 

i-8 

3 

14 

1 
25 

P2 

'i' 

ik 

1 
25 

1 
26 

P3 

■- 

H 
3 

1 

24  THE     MECHANICS     OF     FITTING     GLASSES 

bridge  is  the  distance  above  or  below  a  line  running 
through  the  center  of  the  lenses  to  the  lower  edge  of  the 
center  of  bridge;  the  inclination  of  the  crest  is  the  dis- 
tance from  the  inside  plane  of  the  lenses  to  the  upper 
edge  of  the  middle  of  the  bridge  and  is  specified  "in"  or 
"out,"  meaning  in  back  or  in  front  of  the  lenses,  respect- 
ively. The  angle  of  the  bridge  is  considered  with  respect 
to  the  plane  of  the  lenses,  the  latter  being  90  degrees. 
The  angle  is  measured  at  the  center  or  crest  of  the  bridge. 


Temples. 

The  length  of  temples  is  measured  from  tip  to  tip, 
that  is,  from  the  screw  hole  to  the  extreme  other  end. 
The  average  length  is  six  inches,  but  they  are  also  made 
in  lengths  of  51/2,  6V2  and  7  inches. 


Sizes  of  Lenses. 

"Size  eye,"  as  it  is  familiarly  called,  represents  the 
outside  measurement.  The  regular  sizes  are  jumbo,  0000, 
000,  00,  0,  1,  2  and  3,  beginning  at  the  largest  and  going  to 
the  smallest.  The  "size  eye"  of  frames  agrees  with  the 
size  of  the  lenses. 

"Pupillary  Distance"  is  a  term  so  often  used  in  the 
business  that  we  have  come  to  know  it  familiarly  by  its 
abbreviation,  P.  1).,  so  that  in  this  book  we  shall  always 
refer  to  this  dimension  as  P.  D.  instead  of  writing  the 
words  out  in  full. 


THE      MECHANICS      OF      FITTINC      CLASSES 


25 


The  cut  Oil  this  page  illustrates  a  ineasuring  eard 
used  for  measuring  spectacle  frames.  Your  wholesale 
house  will  supply  you  with  one  of  these  cards. 


•25-*. 


50  60  ^0  TM 

PUPILLARr   DISTANCE 


To  measure  P.  D.  and  height  of  bridge,  place  end 
pieces  on  line  A-A  with  inner  edge  of  left  eye  at  line  B. 
The  figure  at  right  end  of  right  lens  indicates  the  pupil- 
lary distance  and  that  at  under  edge  of  bridge  crest  indi- 
cates the  height  of  bridge. 

To  measure  bridge  crest,  forward  or  back,  place 
lenses  in  slots,  top  down,  with  inner  surface  of  lenses  on 
lower  edge  of  slots.  That  edge  of  bridge  resting  on  card 
will  indicate  position  of  crest. 

It  will  be  noticed  that  in  measuring  the  "pupillary 
width"  of  spectacles  and  eyeglasses,  a  similar  plan  is  fol- 
lowed as  when  measuring  over  the  eyes;  that  is,  the  dis- 
tance is  taken  from  the  nasal  edge  of  one  lens  or  rim 
to  the  temporal  edge  of  the  other  lens  or  rim.  This  is 
most  conveniently  accomplished  by  using  the  ineasuring 
card  designed  for  this  purpose  shown  here. 


26  THE      MECHANICS      OF      KITTING      GLASSES 

Measuring  for  Spectacles. 

Be  sure,  Ijofore  going-  further,  that  you  know  exactly 
all  the  details  already  given,  otherwise  you  will  get  most 
unsatisfactory  results.  For  instance,  you  may  take  the 
base  of  bridge  to  be  from  center  of  the  turns  of  the  shanks 
and  the  optician  who  fills  your  order  will  take  it  from  the 
last  points  where  the  flesh  touches  the  bridge,  with  the 
consequence  that  the  spectacles  you  receive  will  always 
be  from  two  to  thri-e  millimeters  too  narrow.  The  same 
applies  to  all  tli'.'  other  dimensions,  hut  this  is  cited  as 
being  the  most  common  error. 

Provide  yourself  with  a  (i  or  (i'o-incli  rule  gradu- 
ated in  l)otli  inches  and  millimeters;  a  measuring  card, 
and  a  fitting  set  of  spectacle  frames. 

Seat  yourself  directly  in  front  of  the  patient — do  not 
stand,  it  is  awkwai-d  and  conducive  to  error.     Measure 


Spectacle    Fitting    Set. 


THK      MhlCHANK^S      OF      FITTING      GLASSES  27 

the  ])ationt's  I'.  I),  and  note  it  down.  Select  Troni  tlie 
fitting  set  the  hridu'e  tli:it  comes  iieai'est  to  fittiiiii;  the 
patient's  nose.  Notice  the  use  of  tlie  word  ''nearest"  in 
the  i)revious  sentence — it  is  only  once  in  a  hundred  times 
at  least  that  you  will  find  a  stock  size  that  will  exactly  fit. 

Height  of  Bridge. 
Now  for  the  i)roi»er  hridge  dimensions:  AVith  the 
frame,  just  selected,  on  the  patient's  face,  note  whether 
the  lenses  set  too  low  or  too  high,  hearing  in  mind  the  use 
that  tlie  patient  is  going  to  make  of  his  new  glasses, 
whether  for  reading,  distance  or  hoth.  The  average  line 
of  vision  should  he  through  the  center  of  the  lenses.  Sup- 
pose, in  the  case  hefore  you,  the  lenses  in  the  fitting  frame 
set  too  low,  say  one  millimeter.  Now,  if  w^e  move  the 
hridge  down  the  lenses  will  go  up  a  corresponding 
amount,  so  in  this  case,  the  hridge  we  want  should  he  one 
millimeter  lower  than  the  one  on  the  fitting  frame.  Take 
the  frame  from  the  patient's  face  and  measure  the  height 
of  this  hridge;  suppose  you  find  it  to  be  four  millimeters. 
We  found  this  was  one  millimeter  too  high,  so  the  bridge 
we  want  should  be  three  millimeters  in  height.  Mark  it 
down  on  your  prescription  pad. 

Position  of  the  Crest. 

Replace  the  frame  on  the  patient's  face.  Note 
whether  the  lenses  set  too  close  or  too  near  the  eyes. 
Suppose  you  find  the  lenses  touch  the  lashes  and  need  to 
be  set  two  millimeters  farther  out  for  ihe  lashes  to  clear. 

Take  the  frame  off  and  measure  the  position  of  the 
crest  of  this  l»ridge,  using  the  measuring  card  for  this 
purpose.  Suppose  you  find  it  to  be  three  millimeters  out, 
then  as  w^ith  this  bridge  the  lenses  are  two  millimeters  too 


28  THE      .MECHANICS      OF      FITTIXG      GLASSES 

close  to  the  eyes,  the  bridge  we  want  shoukl  be  two  milli- 
meters farther  back  than  it  is,  whieh  gives  us  one  milli- 
meter out  (or  forward)  that  the  bridge  crest  should  be. 
Note  this  down  under  Position  (or  inclination)  of  Crest. 
Width  of  Base. 

Place  the  fitting  frame  on  the  patient's  face,  using  a 
bridge  of  sufficient  width  to  allow  the  crest  to  strike  the 
nose;  push  the  frame  to  the  right  or  left  so  that  all  the 
space  between  the  l)ridge  and  nose  will  be  on  one  side. 
By  ascertaining  how  much  this  space  is  you  know  how 
much  too  wide  the  bridge  is,  and  by  measuring  the  bridge 
and  making  the  deduction  for  oversize,  you  have  the 
projDer  width. 

Pemember,  that  the  base  width  is  measured  from  the 
point  on  each  side  where  the  flesh  last  touches  and  not 
from  the  middle  of  the  turns  of  the  shanks.  The  width 
of  ])ase  is  one  of  the  most  important  dimensions  of  the 
bridge  and  decides  to  a  large  degree  whether  the  spec- 
tacles are  comfortable  or  not.  The  ])ridge  should  tit  the 
nose  just  like  a  saddle,  for  if  it  touches  all  around  it  will 
help  support  the  weight  and  relieve  some  of  the  strain  at 
the  back  of  the  ears.  At  the  same  time  a  bridge  too  nar- 
row at  the  base  will  press  into  the  nose  and  be  very 
uncomfortable. 

Angle  of  the  Crest. 

The  average  angle  subtended  by  the  bridge  of  the 
nose  is  45  degrees,  the  plane  of  the  face  being  DO;  in  other 
words,  the  more  vertical  the  nose  the  higher  will  be  the 
nuniljer  wliich  represents  its  angle.  To  measure  this 
angle  liold  a  i-ulc  oi-  card  pci-pcMidicnlar  to  the  plane  of 
tlie  face  and  note  the  size  of  the  angle  between  the  rule 
and  the  nose  where  the  spectacle  bridge  will  rest. 


THE      MECHANICS      OF      FITTING      GLASSES 


29 


There  are  cards  made  to  take  this  measurement,  as 
well  as  other  littk'  coiitrivaiices.  Here  are  shown  two 
popular  crest  measures. 


Length  of  Temples, 

There  are  two  ways  of  expressing  the  length  of  tem- 
ples desired,  i.  e.,  the  distance  to  hack  of  the  ear  or  the 
entire  length  of  the  temple  from  tip  to  tip.  The  first 
measurement  is  made  with  the  fitting  spectacles  on  the 
patient's  face,  the  two  extreme  points  l)eing  the  plane  of 
the  lenses  and  the  middle  of  the  hack  of  the  ear.  The 
other  method  is  to  notice  how  the  length  of  the  temples 
on  the  fitting  frame  suits,  measuring  the  full  length  of 
these  temples  and  then  adding  to  or  suljtracting  from  this 
length  as  may  be  necessary. 

The  instructions  given  here  api)iy  to  both  rimless 
and  frames.  Some  use  four  or  five  spectacles  of  different 
sizes  to  measure  over,  hut  the  use  of  a  complete  set  of 
12  sizes  is  strongly  advised. 


30 


THE      MEC^HANICS      OK      FITTING      GLASSES 


Eyegl 


asses. 


Finger-Piece.  Regular. 

The  finger-) )i('('('  ty])e  has  eoiiie  into  use  within  tiie 
hist  ten  years  and  on  acconnt  of  neatness  of  api)earance, 
the  property  of  i-etaining  its  original  shai)e  and  adjnst- 
ment,  and  simplicity  in  fitting,  it  has  become  very  popuLar 
and  widely  used.  However,  there  are  cases  where  the 
regular  style  is  more  desirable  than  the  finger-piece  and 
vice  versa.  For  instance,  a  finger-piece  mounting  has  a 
tendency  to  cause  the  nose  to  appear  shorter  and  the  face 
narrower,  while  the  regular  mounting  gives  rise  to  re- 
verse impressions.  This  l)eing  the  case  if  you  put  a 
finger-piece  mounting  on  a  short  nose  you  make  it  seem 
shorter;  a  regular  mounting  would  lengthen  it.  If  you 
fit  a  finger-piece  mounting  where  the  pupillary  distance 
is  comparatively  narrow,  the  eyes  will  seem  still  closer 
together,  whereas  a  regular  mounting  will  seem  to  put 
more  space  between  the  eyes. 

"Regular"  Style. 

To  ascertain  the  correct  size  of  lens,  length  of  stud, 
style  of  gnai'd,  etc.,  it  will  be  (piite  necessary  to  have  an 
eyeglass  mounting  to  measure  over. 

First  measure  the  j)atient's  P.  I).  'IMicn  adjust  your 
sample  mounting  as  well  as  you  can  and  place  it   in  the 


THE      MECHANICS      OF      P^ITTINCJ      GLASSES  31 

correct  position  on  the  patient's  nose.  Now  measure  the 
P.  D.  of  tlie  .glasses  while  on  the  face  (measure  from  in- 
side edge  of  one  lens  to  outside  of  the  other)  ;  this  places 
you  in  position  to  know  liow  large  to  make  the  lenses  and 
how  long  the  studs.  Suppose,  for  illustration,  that  the 
sample  mounting  is  equipped  with  regular  B  studs  and  0 
eye  lenses,  that  your  patient's  P.  D.  is  60,  and  that  the 
P.  D.  of  the  glasses,  when  on,  is  58  millimeters.  You  see 
at  a  glance  that  these  glasses  would  be  too  narrow  and 
their  P.  D.  must  be  increased  2  millimeters. 

There  are  two  ways  in  which  this  can  be  accom- 
plished ;  by  using  longer  studs  or  larger  lenses.  The  next 
size  studs  to  those  on  the  sample  mounting  are  known 
as  C  studs,  there  being  a  ditfereuce  of  one  millimeter  in 
the  length  of  a  B  and  a  C.  By  using  C  studs  in  the  case 
we  are  considering  we  will  increase  the  P.  D.  of  the 
glasses  2  mm.  (Imm.  on  each  stud),  and  thus  obtain  the 
desired  width  of  GO  mm.  By  increasing  the  size  of  lenses 
2  mm.  and  leaving  the  studs  as  they  are  in  the  sample 
(B  size)  we  can  ol)tain  the  same  result.  The  lenses  in  our 
sample  are  0  eye  size  and  their  length  therefore  is 
39  mm. ;  adding  2  mm.  to  this  gives  41,  which  is  the  length 
of  000  eye  lenses,  hence  by  using  000  lenses  and  B  studs 
we  obtain  the  desired  P.  D.  With  these  two  methods  we 
can  make  several  combinations  and  get  exactly  the  dimen- 
sions we  want.  For  instance,  we  have  studs  ranging 
from  A  to  F  (about  1  mm.  difference  for  each  size)  and 
lenses  ranging  from  1  eye  to  jumbo,  or  in  figures,  from 
37  to  46  mm.  long,  which  we  can  combine  in  a  great  many 
different  ways. 

Notice  when  the  mounting  is  in  the  proper  position 
on  the  nose  whether  the  lenses  are  too  close  to  or  too  far 


32  THE      MECHANICS      OF      FITTINC      01. ASSES 

away  from  the  eyes.  If  they  arc  too  close  use  inset  studs 
to  put  them  farther  out,  if  too  far  away  use  outset  studs 
to  bring  them  closer.  Both  of  these  styles  are  made  in 
two  sizes,  1-16  and  1-8  inch,  and  you  can  easily  tell  which 
size  is  required. 

If  the  l)rows  are  prominent  and  press  against  the 
spring  use  a  Grecian  or  a  tilting  spring.  Oblong  springs 
are  usually  used  for  men  and  hoop  springs  for  women, 
but  this  is  a  matter  of  personal  choice. 

The  guards  selected  should  have  a  Hat  surface  where 
they  come  into  contact  with  the  flesh — this  is  the  first 
requisite  of  an  efficient  guard.  In  adjusting  the  guards  it 
must  be  borne  in  mind  that  contact  and  adhesion  count 
greater  for  desirable  results  than  pressure,  and  for  this 
reason  the  guard  must  be  curved  and  bent  to  conform 
with  the  corresponding  part  of  the  nose. 

You  should  have  about  six  eyeglass  mountings,  com- 
plete with  lenses,  and  having  different  styles  of  guards 
and  springs.  With  this  equij^ment  you  can  select  the 
style  of  guard  that  will  be  best  for  each  particular  case. 

Some  styles  and  angles  of  guards  will  set  the  lenses 
lower  than  others,  but  usually  it  is  necessary  to  drill  the 
holes  in  the  lenses  1-16  or  1-S  inch  above  center  to  lower 
them,  especially  wIkm'c  the  glasses  are  to  be  bifocal  or 
reading  lenses,  in  regular  eyeglass  mountings. 

Finger-Piece  Eyeglasses. 

You  must  be  provided  with  a  complete  fitting  set  of 
some  good  make  of  mountings.  Do  not  make  the  com- 
mon mistake  of  getting  a  few  mountings  of  several  kinds, 
but  get  a  full  set  of  some  one  particular  style;  if  they  are 
good  mountings,   with   the   pi'oixT  adjnstmciit,   they   can 


THE      MKCllAXli'S      OF      FITTING      GLASSES  33 

be  inado  to  tit  any  nose  llial  could  wear  eyoo-lasses,  and 
by  gettini;'  a  full  sot  yon  liavo  the  ontifo  rang'o  of  num- 
bers and  sizes  to  select  from. 

With  the  fitting-  set  at  hand,  select  the  mounting  that 
comes  nearest  to  fitting,  take  your  pliers  and  adjust  the 
mounting  so  that  it  will  assume  just  about  the  same  posi- 
tion that  the  mounting  you  order  will  when  adjusted. 
Some  manufacturers  do  not  advise  adjusting  the  mount- 
ings in  tlie  fitting  set,  but  experience  proves  that  it  is  bet- 
ter to  do  this,  for  you  are  then  in  position  to  know  defi- 
nitely whether  the  mounting  can  be  made  to  fit  or  not, 
and  to  accurately  ascertain  the  size  of  lenses  and  the  kind 
of  posts  required. 

Having  decided  what  mounting  fits  the  best,  note  the 
number  it  bears  that  represents  its  size.  Measure  the 
P.  D.  of  the  patient  and  then  measure  the  P.  D.  of  the 
glasses.  If  these  two  measurements  are  alike  prescribe 
the  same  size  lenses  as  those  in  the  fitting  mounting, 
which  is  usually  O  eye  size.  If  the  fitting  glasses  are  too 
narrow  in  P.  D.  increase  the  size  of  the  lenses  until  the 
proper  P.  D.  is  obtained,  provided  of  course  that  it  is  not 
more  than  a  few  millimeters  and  does  not  make  the  lenses 
too  large.  The  00  eye  lenses  are  one  millimeter  longer 
than  0  eye  size  and  will  increase  the  P.  D.  just  one  milli- 
meter; 000  eye  lenses  are  two  millimeters  longer  than  0 
eye  and  will  increase  the  P.  D.  the  same  amount.  You  do 
not  have  to  be  controlled,  however,  by  the  standard  sizes; 
000  eye  lenses  have  a  length  of  -11  mm.,  you  can  use  42,  43, 
or  44  mm.  lenses  if  you  desire.  There  is  usually  about 
9  mm.  diiference  between  the  length  and  breadth  of  regu- 
larly shaped  lenses,  so  you  can  specify  42  x  33  or  43  x  34, 


34  THE      MECHANICS      OF      FITTING      GLASSES 

etc.,  instead  of  trying  to  convert  these  lenses  to  a 
standard  size.  Likewise  where  it  is  desired  to  give  a  short 
oval  effect  you  may  specify  42  x  34  or  42  x  35,  etc.,  but 
always  remember  that  when  you  measure  the  P.  D.  of  a 
pair  of  glasses  you  measure  from  the  inside  edge  of  one 
lens  to  the  outside  edge  of  the  other  lens  and  in  this  way 
the  length  of  only  one  lens  is  included  in  the  total  P.  D. 
and  consequently  au  increase  in  the  length  of  both  lenses 
of  2  mm.  will  increase  the  P.  D.  of  the  glasses  only  2  mm. 
and  not  4  mm.  as  might  at  first  be  supposed. 

Let  us  say  that,  in  order  to  cause  the  glasses  to  have 
the  proper  P.  D.  it  would  be  necessary  to  use  larger  lenses 
than  are  desired.  In  this  case  you  must  use  extended 
posts ;  these  correspond  to  the  G  and  D  studs  in  regular 
eyeglass  mountings  and  are  made  in  just  two  sizes,  1-16 
and  1-8  inch.  Should  you  put  on  1-16  extended  posts  you 
will  increase  the  P.  D.  Vs-i^^^li  or  about  3  mm.  and  %  inch 
extended  posts  would  increase  the  P.  D.  i/4  i^ch  or  about 
6  nun.  Here  it  will  be  seen  that  both  posts  must  be  con- 
sidered in  the  P.  1).  as  we  include  them  both  in  the  P.  D. 
measurement. 

Now  observe  whether  tlie  lenses  are  too  close  or  too 
far  from  the  eyes,  if  so  prescribe  inset  or  outset  posts, 
whichever  are  needed,  the  same  as  when  fitting  regular 
mountings.  Outset  and  inset  |)osts  are  made  in  two 
sizes,  1-16  and  1-8  inch,  and  it  will  l)e  found  compara- 
tively easy  to  judge  which  size  is  needed. 

Summing  up,  the  things  we  need  to  know  in  prescrib- 
ing finger-piece  eyeglass  mountings  are:  The  number  or 
size  of  the  mounting,  extended,  inset  or  outset  posts  and 
the  size  of  the  lenses. 


THE      MECHANICS      OF      FITTING      GLASSES  35 

Fitting  Mountings  and  Frames  to  Contain 
Bifocal  Lenses. 

This  is  one  of  the  most  difficult  branches  of  spectacle 
and  eyeglass  fitting,  and  at  the  same  time  one  of  the  most 
important. 

The  greatest  difficulty  encountered  by  the  wearer  of 
bifocals  is  getting  them  adjusted  high  enough  to  be  able 
to  read  without  turning  the  eyes  way  down  to  escape  the 
upper  edge  of  the  segment  and  yet  low  enough  to  be  able 
to  walk  and  to  see  distant  objects.  Right  here  is  where 
good  judgment  and  ability  to  properly  fit  frames  come 
into  play. 

The  vertical  dimension  of  the  bifocal  segment  should, 
under  average  conditions,  be  just  a  trifle  less  than  half 
the  height  of  the  entire  lens.  The  frame  or  mounting 
should  be  made  so  that,  when  the  patient 's  head  is  upright 
and  his  line  of  vision  is  straight  ahead,  the  upper  edge 
of  the  bifocal  segment  is  on  a  line  with  the  lower  edge 
of  the  patient's  iris.  This,  of  course,  will  be  subject  to 
variation,  according  to  the  distance  the  lenses  set  from 
the  eyes.  If  it  is  necessary  to  set  the  lenses  well  away 
from  the  eyes,  the  lenses  should  be  set  lower  and  if  they 
are  to  be  worn  close  to  the  eyes  they  must  be  set  higher. 

To  tell  just  at  what  height  the  lenses  should  be  placed, 
put  a  pair  of  frames  containing  bifocals  on  the  patient's 
face  and  have  him  look  straight  ahead,  then  hold  your 
hand  down  in  front  of  him  at  about  the  place  he  would 
read  and  instruct  him  to  look  at  it;  note  whether  his  line 
of  vision  in  each  instance  goes  through  the  proper  part 
of  the  lens.    By  moving  the  lenses  up  or  down  you  will 


36  THE      MECHANICS      OF      FITTING      GLASSES 

quickly  see  whether  the  frame  you  have  on  his  face  re- 
quires raising  or  lowering  and  from  this  you  can  judge 
how  you  want  tlie  holes  drilled  or  what  angle  of  guard 
how  high  you  want  the  bridge,  or  in  the  case  of  eyeglasses 
you  need. 

In  cases  where  the  patient  does  a  great  amount  of 
near  work,  it  may  be  found  advantageous  to  use  larger 
bifocal  segments,  but  of  course,  the  larger  the  segment, 
the  more  restricted  will  the  distant  field  be. 

There  are  many  shapes  of  segments,  the  most  com- 
mon being  the  elliptical  and  the  half-round.  Nearly  all 
cement  bifocals  are  of  the  former  shape,  while  Kryptoks 
(invisible  bifocals)  are  usually  about  two-thirds  of  a 
circle.  While  we  are  discussing  Kryptoks  it  may  be  well 
to  state  that  this  form  of  bifocal  is  not  restricted  to  one 
size  and  shape  of  segment.  The  regular  size  Kryptok 
segment  is  about  14  mm.  high  and  18  mm.  across ;  larger 
sizes  can  be  had  as  well  as  the  elliptical,  similar  in  shape 
to  the  regular  cement  bifocal. 

In  your  practice  you  have  come  across  many  people 
who  have  told  you  they  could  not  wear  bifocals  and  you 
have  also  probably  found  that  you  have  been  able  to  sat- 
isfactorily fit  them  with  this  kind  of  lens  by  exercising 
care  in  the  adjustment  of  the  frame  or  mounting,  and  we 
venture  to  say  that  the  majority  of  people  who  say  they 
cannot  wear  bifocals  would  find  the  cause  in  the  faulty 
adjustment  of  the  mounting  rather  than  in  the  construc- 
tion of  the  lenses.  iWith  this  in  mind  we  would  urge  those 
who  have  experienced  difficulty  in  fitting  bifocals  to  make 
a  })jirti('ular  study  of  frame  fitting  in  connection  with 
bifocals. 


How  to  Adjust  Spectacles. 


Before  considering  the  adjusting  of  spectacles  let  us 
analyze  the  conditions  that  must  be  presented  by  a  prop- 
erly fitting  spectacle  frame  or  mounting.  The  lenses 
must  center  before  the  eyes  and  sit  just  as  close  as  pos- 
sible to  the  eyes  without  touching  the  lashes.  In  glasses 
that  are  to  be  used  for  general  work,  i.  e.,  both  distant 
and  near,  the  line  of  vision  should  be  just  a  trifle  above 
the  center  of  the  lenses  when  the  eyes  are  directed 
straight  ahead.  Every  part  of  the  frame  must  give  entire 
comfort;  the  bridge  must  fit  all  around  the  curve  of  the 
nose  like  a  saddle  on  a  horse's  back,  and  the  temples 
must  be  just  the  right  length.  Bear  all  the  foregoing  in 
mind  when  fitting  spectacles  and  the  results  will  in- 
variably be  decidedly  better  than  when  some  of  these 
points  are  ignored. 

There  are  pliers  that  are  specially  designed  to  do 
particular  kinds  of  work,  and  it  will  be  advantageous  to 
be  supplied  with  the  proper  tools  and  to  know  their  re- 
spective uses,  for  you  cannot  accomplish  satisfactory 
results  when  you  are  not  properly  equipped  in  this 
regard.  The  following  styles  of  pliers  are  necessary  in 
adjusting  spectacles:  Snipe-nose  (half  round),  full 
round,  concavo-convex,  bridge  angling,  and  stud  pliers. 
There  are  other  styles  that  will  facilitate  the  work,  but 
these  just  enumerated  are  absolutely  needed. 

37 


38  THE      MECHANICS      OF      FITTING      GLASSES 

Miieli  practice  will  be  re(|uired  })efore  you  will  be 
able  to  do  justice  to  a  bridge  iu  the  matter  of  bendiug,  and 
it  is  suggested  that  you  make  use  of  all  available  old 
frames  or  even  buy  some  cheap  frames  to  practice 
bending,  etc. 

Adjusting, 

If  the  lenses  are  too  high  and  it  is  desired  to  lower 
them  bend  the  shanks  of  the  bridge  downward,  but  re- 
member that  in  doing  this  you  will  lower  the  angle  of  the 
bridge  and  allowance  must  be  made  for  this.  If  the  lenses 
are  too  low  bend  the  shanks  upward,  remembering  that 
this  will  also  alter  the  angle  of  the  bridge. 

The  angle  of  the  bridge  may  be  varied  by  angling  the 
crest  with  ordinary  snipe-nose  pliers  or  by  curving  the 
shanks  upward  or  downward  at  the  eyewire  or  strap,  but 
the  best  way  is  to  use  pliers  that  are  especially  made  for 
angling,  for  instance,  the  Berg  pliers,  by  means  of  which 
the  angle  can  be  changed  properly  in  a  very  short  time. 

The  shanks  may  be  lengthened  or  shortened  to  con- 
trol the  distance  of  the  lenses  from  the  eyes  by  changing 
the  relative  position  of  the  point  at  which  the  bridge 
curves  to  make  the  shanks.  First,  with  a  pair  of  snipe- 
nose  pliers  flatten  out  the  curve  in  the  shank,  then  with 
a  pair  of  full  round  pliers  put  the  bend  in  the  bridge  just 
where  you  want  the  shanks  to  begin  and  continue  to  bend 
the  shanks  over  until  they  are  brought  into  the  proper 
position.  It  is  (piite  essential  that  pliers  with  full  round 
jaws  l)e  employed  for  making  these  curves  as  the  other 
pliers  will  mark  and  cut  the  covering  of  the  bridge. 

T\\r   pupillary   width   of  the  glasses  should   be  con- 


THE      MECHANICS      OF      FITTING      GLASSES  39 

trolled  l)y  the  direction  taken  by  the  shanks  without  dis- 
turbing the  width  of  the  base  of  the  bridge. 

The  width  of  the  base  should  l)e  altered  l)y  using 
pliers  that  have  one  jaw  concave  and  the  other  convex. 
Changing  the  base  will  also  affect  the  pniiillary  width. 
In  bending  a  bridge  it  will  be  wisest  to  ascertain  just  ex- 
actly what  alterations  are  necessary  before  making  any, 
due  to  the  fact  that  every  dimension  is  dependent  upon 
the  other  and  a  change  in  one  will  cause  a  corresponding 
change  in  some  of  the  others. 

To  bend  temples  so  as  to  angle  the  lenses  or  where 
one  ear  is  higher  than  the  other  and  one  temple  must  l)e 
raised  use  two  pairs  of  pliers;  with  stud-pliers  grasp  the 
end-piece  close  to  the  edge  of  the  lens  or  eyewire  and  with 
a  pair  of  snipe-nose  pliers  take  hold  of  the  outside  end  of 
the  end-piece  and  bend  the  part  of  the  end-piece  to  which 
the  temple  is  attached  so  as  to  move  the  temple  upward  or 
downward  as  may  be  desired;  in  other  w^ords  the  end- 
piece  is  slightly  twisted.  Above  all  things  do  not  curve 
or  bend  the  temple  itself,  but  confine  your  bending  to  the 
end-piece. 

To  curve  the  temples  for  the  turn  of  the  ear  use  a 
pencil  or  something  else  round  and  curl  the  temple  as  you 
would  a  feather,  by  drawing  the  end  of  the  temples  be- 
tween your  thumb  and  the  pencil.  Temples  may  be  curved 
outward  in  a  similar  manner  where  they  cut  into  the  flesh 
on  the  side  of  the  face. 

If  you  find  one  lens  sits  higher  than  the  other  it  may 
be  that  one  ear  is  higher  than  the  other  and  the  trouble 
should  be  rectified  by  angling  the  temples  as  already  ex- 
plained in  next  to  the  last  paragraph. 


How  To  Adjust   Eyeglass 
Mountings. 


We  shall  consider  here  two  kinds  of  eyeglass  mount- 
ings in  general,  that  is,  those  of  the  tinger-pieee  type  and 
those  with  the  regular  hoop  springs.  In  differentiating 
between  these  two  kinds  the  spring  of  the  regular  and  the 
bridge  of  the  finger-piece  mounting  are  the  essential 
l)oints  and  the  same  rules  wnll  apply  to  both  classes  of 
mountings  except  wliere  they  apply  to  these  two  conflict- 
ing portions. 

The  first  aim  in  fitting  the  eyeglass  is  to  make  it  stay 
on  securely  with  comfort,  and  in  effecting  this  we  cannot 
sacrifice  correctness  of  position,  so  tliat  many  times  we 
are  confronted  with  a  complex  problem  when  we  endeavor 
to  make  these  three  features  work  harmoniously.  Let 
us  first  reason  out  the  proper  means  of  holding  the 
mounting  securely  on  the  nose.  Before  we  go  farther 
try  this  experiment  and  get  it  impressed  firmly  upon  your 
memory:  Place  the  palms  of  your  hands  together  and 
administer  a  slight  pressure;  notice  when  you  do  this  that 
it  requires  considerable  force  to  slide  your  hands  a^iart. 
Now  place  the  backs  of  your  hands  together  and  observe 
liow  hard  you  have  to  press  to  make  it  difficult  to  slide 
your  hands  on  each  other.  Why  is  this  so?  It  is  so  be- 
cause in  the  case  of  your  i)ahiis  being  laid  together  they 
presented  a  multiplicity  of  contact  points,  one  fitted 
closelv  into  the  other  and   they  adhered  to  each  otlier. 


4U 


THE      MECHANICS      OF      FITTING      GLASSES  41 

Apply  this  same  sort  of  thing  to  the  eyeglass  guard  and 
you  have  solved  l)oth  the  pro])lein  of  holding  the  glasses 
on  securely  and  that  of  making  it  comfortahle. 

The  guards  themselves  must  present  a  smooth  sur- 
face to  the  flesh  and  must  be  curved  so  as  to  conform  to 
the  contour  of  the  portion  of  the  nose  over  which  they 
rest.  To  curve  the  guards  in  this  manner  it  is  quite  es- 
sential to  have  the  proper  kind  of  pliers ;  the  best  for 
this  purpose  are  those  that  have  one  convex  blade  and 
one  concave  so  that  by  simply  pressing  the  blades  to- 
gether the  portion  of  the  guard  on  which  you  are  working 
assumes  a  corresponding  curvature  in  degree  depending 
on  the  amount  of  pressure  you  give  the  pliers.  By  using 
pliers  of  this  kind  the  guards  may  be  accurately  curved 
without  interfering  in  any  way  with  the  remainder  of  the 
guard  or  its  general  angle,  etc.  Suppose  now  after  you 
have  given  the  guards  the  proper  curvature  and  granting 
the  other  parts  of  the  mounting  are  evenly  balanced  and 
straight,  that  one  lens  is  higher  than  the  other.  This  is 
a  trying  puzzle  to  every  beginner  and  to  many  who  have 
been  in  the  business  a  long  time.  We  will  say  for  instance 
that  the  left  lens  is  higher  than  the  right.  Take  the 
curved  pliers  and  bend  the  bottom  of  the  left  guard  out 
slightly,  being  careful  not  to  bend  it  so  far  that  it  leaves 
the  flesh.  If  this  is  not  sufficient  to  lower  the  lens,  bend 
the  entire  guard  on  its  axis  so  that  the  bottom  portion 
does  not  press  so  hard;  this  will  bring  the  top  of  the 
guard  in  tighter,  but  care  must  be  exercised  not  to  bring 
this  in  too  tight.  Further  lowering  of  the  left  may  be 
accomplished  by  raising  the  right  lens,  which  is  done  by 
bending  the  right  guard  in  toward  the  nose  slightly  at 
the  bottom.     It  is  surprising  how  bending  of  the  guards 


42  THE      MECHANICS      OF      FITTING      GLASSES 

will  t'lTcc't  tlie  respL'ctivo  lici^vhts  of  the  lenses.  As  was 
said  at  the  beginning  security,  comfort  and  correctness 
of  position  must  all  obtain  to  tiie  fullest  possible  degree 
and  one  must  not  be  sacriliced  for  the  others. 

In  all  cases  the  top  of  the  guard  should  be  curved  out 
slightly  to  agree  with  the  curvature  of  the  nose  as  it 
merges  into  the  ))rows,  if  this  curving  is  not  done  here 
the  top  of  the  guard  will  cut  into  the  flesh  and  prove  very 
uncomfortable.  Jt  is  the  bottom  of  the  guard  that  sup- 
ports the  weight  of  the  glasses  and  the  top  that  prevents 
them  from  tilting  over,  so  that  the  top  of  the  guard  must 
necessarily  press  a  trifle  harder  than  the  l)ottom,  and  as 
a  general  thing  more  pressure  can  l)e  stood  here  than 
at  the  bottom  because  there  is  nearly  always  a  little 
cushion  of  flesh  here.  Wherever  the  guard  rests  on  a 
bony  part  of  the  nose  the  contact  must  be  very  even  and 
the  pressure  comparatively  light,  else  the  guard  will  cut 
the  skin.  By  giving  the  guards  the  same  curve  as  the 
nose  they  will  stick  to  the  skin  and  much  less  pressure 
will  be  required  than  otherwise.  Another  good  plan  is 
to  bend  the  entire  guard  out  from  the  back  so  that  there 
is  more  pressure  along  the  front  or  outside  edge  of  the 
guard  than  in  the  back;  this  will  cause  the  flesh  to  pile 
up  slightly,  as  it  were,  in  front  of  the  guard  and  form  a 
wedge  of  the  flesh  which  prevents  the  mounting  from 
slipping  forward. 

In  the  case  of  a  regular  mounting  with  the  hoop 
spring  sometimes  it  is  desirable  to  have  the  spring  tilting 
slightly  at  the  to])  away  from  the  forehead  on  account 
of  licaxy  lnows  oi-  high  nose.  There  ai"e  s])rings  that 
are  made  with  this  tilt  but  if  the  mounting  you  are  ad- 
justing is  not  tilting  and  you  would  pi'efer  to  have  it  so 


THE      MECHANIC'S      OF      FITTING      GLASSES  43 

you  can  very  easily  hciid  it  to  liavc  the  desired  tilt.  To 
do  this  nse  ^Yllat  is  known  as  stud  [(licrs,  taking'  tlieiu  in 
one  hand  and  gripping-  the  straj)  of  one  of  the  studs  with 
them.  Grip  the  pUers  tightly  and  with  the  thumb  of  your 
other  hand  press  against  the  top  of  tlie  spring  and  you 
will  find  that  you  can  bend  it  outward.  After  doing  this 
take  liold  of  the  other  stud  with  the  pliers  in  a  similar 
way  as  before  and  repeat  the  operation  on  this  side,  thus 
evening  u})  the  tilt  from  both  sides.  It  will  be  w^ell  to 
practice  this  so  that  when  >()U  want  to  do  it  you  are  sure 
that  you  know  what  you  are  doing  and  it  will  prove  ({uite 
valuable  in  getting  a  good  tit  many  times,  for  often  the 
mounting  cannot  be  set  far  enough  back  on  the  nose  due 
to  protruding  brows. 

When  placing  eyeglasses  on  a  patient's  nose  do  not 
hold  the  glasses  by  placing  your  fingers  on  the  two  sides 
of  the  lenses,  Init  allow  your  fingers  to  touch  only  the 
edges  of  the  lenses.  This  keeps  the  lenses  clean,  elimi- 
nates the  possibility  of  sticking  your  finger  in  the  pa- 
tient's eye  and  is  not  so  awkward  as  the  other  way. 

In  handling  finger-piece  mountings  do  not  grasp  the 
finger-pieces  with  the  thumb  and  forefinger,  but  use  the 
thumb  and  middle  finger  and  press  the  forefinger  against 
the  bridge;  this  steadies  the  mounting  and  gives  you  a 
secure  hold  on  it.  Your  patients  should  be  instructed  to 
take  hold  of  the  mountings  in  the  same  manner. 

If  the  guards  are  covered  with  shell,  be  sure  to 
smooth  off  the  edges  all  around,  using  a  fine,  flat  file  for 
the  purpose.  It  w^ill  often  be  found  in  cases  w^here  the 
mounting  is  not  comfortable  and  the  guards  are  covered 
with  shell  or  a  similar  substance  that  the  trouble  can  be 
relieved  by  filing  the  edges  of  the  shell  on  the  guards. 


44  THE      MECHANICS      OF      FITTING      GLASSES 

Wheii  mountings  contain  toric  lenses  the  efficiency 
of  the  lenses  may  be  increased  by  bending  the  lenses  in 
toward  the  temples.  This  enables  the  patient  to  look 
sideways  without  being  annoyed  by  the  edges  of  the 
lenses. 

One  of  the  chief  objections  to  finger-piece  mountings 
is  that  they  are  apt  to  sit  too  high  and  to  sit  farther  from 
the  face  at  the  bottom  of  the  lenses  than  at  the  top. 
Great  care  must  be  exercised  to  prevent  these  two  con- 
ditions and  it  will  be  well  for  you  to  understand  how  to 
overcome  these  difficulties.  The  standing  away  from  the 
face  at  the  bottom  of  the  lenses  can  be  rectified  by  spread- 
ing the  guards  at  the  bottom  and  l)y  making  them  incline 
somewhat  from  the  vertical.  The  custom  of  bending  the 
ends  of  the  bridge  downward  and  drilling  the  holes  above 
center  is  not  advised  in  cases  where  it  is  desired  to  set 
the  lenses  lower,  because  it  spoils  the  appearance  of  the 
mounting,  narrows  the  base  of  the  bridge  and  disrupts 
the  proper  working  of  the  springs  and  finger-pieces. 
The  better  plan  would  be  to  fit  mountings  in  which  the 
guard-arms  are  so  constructed  that  the  guards  may  be 
raised  without  changing  their  angle  or  mountings  that 
are  supplied  with  drop-studs  or  "tangent"  studs,  as  they 
are  called  by  some.  To  increase  the  tension  of  springs 
on  finger-piece  mountings  detach  the  long  end  of  the 
spring,  gripping  it  with  a  pair  of  pliers,  and  pull  the 
spring  tighter  on  the  coil.  To  decrease  the  tension  push 
back  on  the  coil.  In  cases  of  springs  of  the  lever  variety 
in  which  it  is  not  possible  to  adjust  the  tension  of  the 
coil,  l)en(l  the  long  i'vvo  end;  to  increase  the  tension  bend 
it  toward  the  side  it  presses,  to  decrease,  press  toward 
the  opposite  side. 


THE      MECHANICS      OF      FITTING      GJ.ASSES 


4.-) 


Pliers  You  Need. 


Full    Round. 


Half   Round    (Snipe    Nose). 


Cutting. 


Stud. 


46  THE      MECHANICS      OF      FITTING      GLASSES 

0 


Angling. 


Concavo-convex. 


Strap. 


How  to  Judge  a  Good  Finger- 
Piece  Eyeglass  Mounting. 


The    two    main    things    for    consideration    are    the 
springs  and  the  guards.     There  are,  in  general,  three 
kinds  of  springs — coil,   lever,  and  ribbon  or  flat;  these 
are  seen  at  times  in  combination  and  there  are  variations 
of  each  kind.    In  the  spring  we  look  for  constancy,  dura- 
bility, and  strength.     In  other  words  the  spring  should 
maintain  an  even  pressure  for  a  considerable  time  and 
not  be  likely  to  come  off  easily.    Coil  springs  are  the  ones 
most  likely  to  give  trouble,  especially  if  both  ends  are 
attached  to  the  mounting;  if  one  end  is  left  free  there  is 
less  likelihood  of  the  spring  playing  out.    Now  then  for 
the  guard :    The  requisite  of  a  good  guard  is  that  it  pre- 
sent a  smooth,  flat  surface  to  the  flesh  over  a  generous 
space,  for  a  guard  will  hold  with  much  greater  comfort 
and  less  pressure  if  its  powers  of  adhesion  are  well  de- 
veloped.    To  understand  better  just  what  is  meant  by 
this  place  the  palms  of  your  hands  together  and  see  how 
with  a  little  pressure  it  is  quite  difficult  to  slide  them  on 
each  other;  now  place  the  backs  of  your  hands  together 
and  you  will  find  that  although  you  apply  a  great  deal 
of  pressure  you  can  slide  them  with  ease.     Guards  that 
are  built  like  a  crab's  claw  with  twists    and   turns  and 
parts  touching  here  and  there  are  by  no  means  efficient, 
and  there  are  many  guards  on  the  market  just  like  this 

47 


48  THE      MECHANICS      OF      FITTING      GLASSES 

— avoid  lliciii  if  you  want  your  ])ati('nts  to  wear  the 
glasses  you  give  them  with  coinfort. 

Another  point  for  careful  attention  is  the  manner 
in  which  the  guard  is  attached  to  the  mounting  and  range 
of  adjustments  the  general  ('()ml)inaiioii  offers.  If  the 
guard  is  so  attached  that  it  cannot  be  moved  higher  or 
lower  and  closer  or  farther  away  from  the  bridge  and 
the  angle  of  the  guard  cannot  be  changed  without  inter- 
fering with  the  workings  of  the  spring,  the  mounting 
should  be  discarded  for  one  that  does  offer  these  neces- 
sary adjustments.  Most  of  the  standard  mountings  can 
be  had  in  what  is  known  as  oft"set,  inset,  and  extended 
posts,  so  as  to  accommodate  cases  where  the  nose  is  ex- 
ceptionally high  or  low  or  where  the  P.  I),  is  wide  and 
the  nose  narrow;  any  mounting  that  cannot  he  had  in 
these  styles  is  not  a  good  one  to  adopt. 

Right  here  it  might  be  well  to  repeat  that  it  is  rec- 
ommended that  you  adopt  one  or  two  good  styles  of  tin- 
ger-piece  mountings,  have  a  complete  fitting  set  of  each 
and  use  these  exclusively  when  fitting  mountings  of  this 
type,  for  if  you  have  one  or  two  good  styles  of  mountings 
and  the  full  range  of  sizes  from  which  to  choose  you  will 
be  able  to  fit  any  case  where  it  is  at  all  possible  to  fit  an 
eyeglass.  The  fitting  sets  should  be  kept  intact  and  com- 
plete always  and  the  mountings  should  contain  lenses, 
for  w^ithout  these  it  is  difiicult  to  tell  just  how  a  mounting 
will  set  and  ))esides  they  offer  a  means  indicating  the  dif- 
ferent sizes  of  mountings  by  having  the  size  of  the  mount- 
ing <'t('h(Ml  on  them  instead  of  having  to  use  tags  on  the 
mountings,  which  are  constantly  in  the  way  and  have  a 
very  bad  appearance. 


How  to  Write  Prescriptions 
to  Be  Sent  to  the  Shop. 

This  is  one  of  the  most  important  chapters  in  this 
book  and  should  receive  very  careful  attention.  A  full 
understanding  of  the  connnon  terms  used  in  the  optical 
business  and  a  knowledge  of  the  construction  of  the  vari- 
ous kinds  of  lenses,  frames,  mountings  and  parts,  etc.,  is 
positively  necessary,  and  it  is  just  as  essential  to  know 
the  common  names  for  the  various  parts  and  operations 
as  it  is  to  know  of  their  construction,  for  without  this  you 
will  be  unable  to  order  and  get  just  what  you  want.  One 
good  plan  is  to  take  the  general  catalog  of  some  standard 
wholesale  house  and  study  it  as  you  would  one  of  your 
most  important  text-books.  If  it  were  possible  for  you 
to  spend  about  two  hours  in  the  prescription  department 
of  any  wholesale  optical  house  you  would  soon  appreciate 
the  importance  to  you  of  knowing  how  to  order  so  that 
the  man  who  fills  the  order  will  thoroughly  understand 
what  you  want  without  taking  chances  at  guesses  and 
having  to  figure  out  some  kind  of  enigma  or  some  long- 
winded  description.  Eemember  that  an  order  for  a  pair 
of  special  lenses,  for  instance,  has  to  pass  through  the 
hands  of  several  people,  and  if  your  orders  are  not  clear 
and  concise  each  man  has  to  waste  a  great  deal  of  time 
deciphering  your  specifications,  thus  delaying  your  work 
and  that  of  others.    As  far  as  possible  in  describing  the 

49 


50  THE      MECHANICS      OF      FITTING      GLASSES 

style  of  fraiiu's  or  iii()iiiitiii,<»s  cataloii,'  luuiihers  should  be 
used.  The  followiiii;'  is  an  exanii)le  of  a  i)re8cription 
received  by  a  wholesale  house  fi'oin  a  man  who  thought  he 
knew  all  about  oi)ties  and  fitting  glasses  and  took  offense 
when  corrected:  The  formulas  for  l)oth  distance  and 
near  were  entered  on  the  l)lank  and  this  note  appeared 
below:  "Put  scales  on  the  inside;  but  L  do  not  want 
bifocals."  Another  Kx  gave  the  formulas  for  both  dis- 
tance and  near  without  any  explanation  regarding  what 
kind  of  lenses  were  desired  and  the  natural  inference  w^as 
tliat  bifocals  were  wanted,  and  so  in  accord  with  the  cus- 
tom the  regular  cement  bifocals  were  supplied.  From  a 
letter  from  this  customer  the  house  learned  that  he  did 
not  want  bifocals,  but  simply  lenses  for  reading.  But 
how  were  they  to  know!  It  is  really  surprising  how  few 
men  know  liow"  to  tell  the  wholesale  house  just  what  they 
want,  but  it  is  just  the  people  who  do  not  know  how  to 
order  who  experience  the  greatest  trouble  and  delay  and 
who  are  the  most  unreasonable  when  they  do  not  receive 
what  they  tliought  "the  wholesale  house  surely  ought  to 
know  what  they  wanted, ' '  The  instructions  given  in  this 
chapter  refer  mostly  to  orders  sent  in  for  filliuf/,  records 
having  been  discussed  in  another  section. 

Fundamental  Rules. 

Use  a  separate  blank  for  each  order  or  each  pair  of 
glasses.    Write  clearly  and  avoid  vague  descriptions. 

Nevei'  use  ink  or  indelible  pencil  to  write  prescrip- 
tions that  you  send  to  the  wholesale  house  foi-  fiHing,  as 
this  Rx  accompanies  the  job  in  its  journey  through  the 
shop,  and  as  water  is  used  in  grinding  the  lenses  this 
gets  on  Ihe  pa[)er  and  runs  the  ink,  making  it  illegible. 


THE      MECHANICS      OF      FITTIXC.      GLASSES  51 

When  oi-deriii.i;-  lenses  he  sure  to  state  size  oi'  eye  and 
whether  rimless  or  for  I'lanies. 

(rive  each  Kx  a  nuniher  or  i)atient's  name  and  the 
date. 

Sign  yonr  name  at  the  hottom.  The  iionse  may  rec- 
ognize your  handwriting,  hut  most  likely  not,  for  your  Rx 
is  one  among  from  500  to  1,000  received  daily. 

Do  not  write  instructions  across  ])rinted  matter,  as 
this  makes  tliem  very  diftieult  to  read. 

Name  or  Number. 

It  is  well  to  give  each  order  a  name  or  number,  which 
will  be  useful  when  writing  about  an  order  or  for  other 
future  reference. 

Formulas  of  Lenses. 

When  the  usual  form  is  followed  of  writing  the 
sphere  first,  the  cylindrical  value  next,  and  the  axis  of 
cylinder  next,  it  is  not  necessary  to  append  the  abbrevia- 
tions "Sph.,"  "C'yl.,"  or  "axis,"  even  when  not  written 
on  a  tabulated  blank,  in  which  case  the  form  should  be 
thus :  — 1.50  —  .75  X  90. 

When  distance  lenses  only  or  reading  lenses  only  are 
wanted  give  the  formula  for  the  particular  correction  you 
want  and  not  both.  When  both  formulas  are  given,  as 
in  cases  where  bifocals  are  desired,  it  is  best  to  give  the 
total  reading  correction  in  full  and  not  the  addition  for 
the  bifocal  portion.  In  such  cases  where  the  addition  is 
given  you  must  be  very  particular  to  append  the  word 
"Add"  after  the  amount  to  be  added.  It  is  because  it  is 
so  easy  to  forget  to  affix  this  little  word  that  it  is  much 


52  THE      MECHANICS      OP^      KITTING      GLASSES 

bettor  to  always  "ivc  tlio  full  reading  eorreetion  after 
the  addition  lias  l)eeii  made;  get  into  tlie  habit  of  doing 
this  and  yon  will  avoid  many  mistakes  and  misunder- 
standings. 

Other  Lens  Specifications. 

Always  state  whether  yon  want  "toric"  or  "flat" 
lenses.  While,  sti'ietly  speaking,  there  is  no  such  thing 
as  a  "spherieal  toric,"  the  correct  term  being  "menis- 
cns,"  the  term  "toric"  is  generally  accepted  as  applying 
to  all  lenses  constrncted  on  a  deep  periscopic  base.  By 
"flat"  lenses  is  meant  all  lenses  that  are  not  toric  (or 
meniscus). 

Give  the  "size  of  eye"  in  the  proper  space;  this  is 
the  size  of  lens  as  has  been  described  in  another  part  of 
this  book. 

When  lenses  only  are  being  ordered  and  you  do  not 
want  them  put  into  a  frame  or  mounting,  be  sure  to 
state  whether  they  are  to  l)e  rimless  or  inserts  (for  rims), 
and  if  rimless  how  many  holes  you  want  drilled  in  them. 
In  specifying  for  the  drilling  of  holes  always  specify  the 
number  of  holes  i)er  pair,  even  in  cases  where  only  one 
lens  is  ordered. 

Should  you  ordei-  just  a  single  lens  and  do  not  send 
the  other  lens  to  be  matched  for  thickness,  be  sure  to  give 
the  thickness  of  the  lens  at  the  "strap,"  or,  in  other 
words,  where  it  is  attached  to  the  mounting.  This  thick- 
ness may  l)e  ascertained  by  measuring  with  a  millimeter 
rule  oi'  l)y  using  a  sti'aj)  gauge. 

if  you  do  not  gixc  any  instructions  regarding  how  the 
holes  shall  be  di-illcd  tlicy  will  be  drilled  "on  line";  in 
cases  where  von  want  ilic  lenses  to  set  lower  when  usinsr 


THE      MErHAXICS      OF      FITTING      GLASSES 


53 


eyeglass  moimtiiii's,  si.ecit'y  that  you  want  the  holes 
drilled  above  center,  stating  how  ninch,  thus:  Drill  one- 
eighth  al)Ove,  or  drill  one-sixteenth  ahove,  as  the  ease 
Tuay  I'eiiiiire. 

The  Frame  or  Mounting. 
Know  just  what  you  want  heiv  and  give  six'cifie  in- 
structions, for  tliis  part  of  the  order  is  just  as  important 
as  that  part  which  refers  to  the  lenses;  renienil)er  the 
man  who  fills  your  order  does  not  see  the  patient  and 
must  have  definite  dimensions  l)y  wliich  to  he  guided  if 
he  is  to  make  up  a  frame  or  mounting  that  will  fit. 

Eyeglasses. 

In  the  proper  space  state  what  style  of  mounting  you 
desii-e  and  what  kind  of  material  you  want,  such  as  gold 
filled,  solid  gold,  nickel,  etc.  As  far  as  possible  it  is  well 
to  give  catalog  or  stock  nimibers  becanse  these  are  qnickly 
reiCd  and  nnderstood,  save  space  on  the  order  blank  and 
save  time  in  the  shop.  AVhen  ordering  finger-piece 
mountings  remember  that  the  numbers  given  in  your  fit- 
ting set  refer  to  size  of  the  bridge  only  and  not  to  the 
particular  style  of  mounting.  For  instance,  let  us  say 
you  are  fitting  from  a  set  of  mountings  known  as  the 
"-Stavthere  Mountings,"  and  you  decide  that  a  No.  842 
is  the  size  vou  desire  and  the  patient  orders  gold  filled, 
on  vour  order  you  would  specify  -G.  F.  Stay  there  842." 
Thus  vou  cover  every  point  of  style  wanted,  so  that  the 
man  wdio  fills  your  order  knows  positively  just  what  you 
want.  Figure  out  exactly  what  size  lenses  you  want;  do 
not  give  the  pupillary  distance  and  the  bridge  number 
amrexpect  the  workman  to  figure  out  the  size  lens  re- 


54  THE      MECHANICS      OF      FITTING      GLASSES 

quired,  because  while  it  would  he  possil)le  for  him  to  do 
this,  remember  tliat  th.^  man  who  grinds  the  lenses  does 
not  i)iek  out  the  mounting  or  adjust  it  to  the  lenses,  and 
the  preserijjtion  clerk  has  t(»  figure  it  out  and  mark  it  on 
the  order  before  it  goes  into  the  shop,  and  probal)ly 
rather  than  delay  the  other  orders  that  are  all  properly 
written  he  will  lay  your  order  to  one  side  until  the  others 
are  passed  into  the  shop,  thus  delaying  the  filling  of  your 
order.  It  will  take  you  but  a  moment  to  decide  what  size 
lenses  you  need  and  to  mark  it  down  on  the  order,  so 
in  your  own  interest  do  this.  Rememl)er  that  UOO  eye  size 
is  just  one  millimeter  longer  than  (ID  eye,  and  that  00  eye 
is  just  one  millimeter  longer  than  0  eye,  and  each  change 
of  eye  size  will  make  just  one  millimeter  difference  in 
the  pupillary  width  of  the  glasses.  Tn  ordering  eye- 
glasses of  the  finger-piece  type  the  only  data  necessary 
are : 

Material,  Style,  Size  of  Mounting  and  Size  of  Lenses. 
Pupillary  width  and  "Spread  of  Guards"  are  superfluous 
when  ordering  any  kind  of  eyeglass  mountings  or  frames, 
because  the  pupillary  width  will  l)e  controlled  by  the  size 
of  lens  and  size  of  mounting,  and  the  "Spread  of  Guards" 
will  have  to  be  effected  by  you  when  you  fit  the  mounting 
to  the  patient's  face,  for  eyeglass  guards  cannot  be 
adjusted  "by  mail";  the  i)atient  must  be  right  in  front 
of  you  at  the  time. 

]\Iost  of  the  foi-egoing  applies  to  finger-piece  mount- 
ings; hooi)  spring  mountings  must  l)e  oi-dered  in  a  some- 
what different  manner.  Give  the  kind  of  material,  size 
of  lenses,  size  and  style  of  stnds,  style  of  guards,  size 
and  style  of  sjjring.  This  iiif'oi-mat  ion  definitely  stated 
will  get  you  Just  exactly  what  you  want. 


THE      MECHANICS      OF      FITTING      GLASSES 


Specimen  of  the  Usual    Form  of  Rx    Blank    Supplied  by 

Wholesale  Optical  Houses,  Containing  an 

Order  for  Spectacles. 

42^ 


PATIENT 


B 


NO. 


SPH.                j                 CYL.                 1       AXIS        1     PRISM 

BASE 

LERS  INtTRUCTIOIIS 

w  -  ^/ 

h  .p^s^         <90 

l\  --h/. 

f-.^^a     /ySX) 

(3)-  - 

MARK   A  CIRCLE  AROUND  STYLE  WANTED  AS    INDICATED   BELOW    . 

DRILLING 

KRYPTOK  1     PERFECTION 
BIFOCAL   1           BIFOCAL 

^ 

^"^  pE^Tr-^r 

PER    PAIR 

ibovt  Ctntir    BelowCinlir 

FRAME  INSTRUCTIONS; 

-^/:i<=)  -/o/^. 


IV^EVE    ooo 

BRIDGE 
NUMBER 

PUPILLARY           X,    •^ 
DISTANCE             %£/    C/ 

s 

BRIDGE   J 

HEIGHT 

POSITION   OF  CREST 

AngleofCrest 

WIDTH    AT    BASE 

U    J 

z  u 

0  < 

*? 

.— 

"" 

y^Xf 

/<f^ 

I  a 

0 

TEMPLES 

oTi:: '° "'" 

If^STM 

6" 

*o,nt'  °'' 

K  iS  (  SPREAD  Ql 

F  GUARD 

STYLE  or  POST 

STVLCOPOUAKO 

STVLEOPSPRma 

11 

AT  TOP          [ 

REMA 


56  thp:    mp:chaxics    of    fitting    glasses 

Spectacles. 

State  the  style  of  t'l'ami'  or  iiiDUiiting  and  wh'.it  kind 
of  material  wanted,  the  size  eye,  ])npillary  width;  give  the 
bridge  dimensions  regarding  height  and  position  of  crest 
either  in  fignres  or  by  a  l)ridge  number;  state  the  angle 
of  crest  and  width  of  base.  The  length  of  temple  may 
be  expressed  either  by  giving  the  total  length  from  tip 
to  tip  or  by  giving  the  distance  in  a  straight  line  from  tlie 
plane  of  the  lens  to  the  middle  of  the  liack  of  the  ear;  the 
former  is  preferaV)le,  l)ecanse  it  is  detinite.  The  style  of 
temple  should  be  stated  at  the  same  time  you  are  speci- 
fying the  style  of  the  mounting. 

There  are  stock  sizes  of  bridges  that  have  stated 
dimensions  and  these  various  sizes  are  designated  by 
letters,  such  as  At,  N,  (),  etc.  AVhere  the  dimensions  of 
the  bridge  wanted  are  not  given  in  figures  the  letter  rep- 
resenting the  size  desired  may  be  given  in  the  space  on  the 
blank  usually  headed  "Bridge  Number";  it  is  much  more 
desirable  to  give  the  dimensions  in  figures,  however,  as 
this  insures  a  well  fitting  bridge.  Where  the  letter  is  used 
to  denote  the  size  of  bridge  wanted  it  is  not  necessary  to 
enter  the  figures  for  Height,  Position  of  Crest  or  Base, 
as  these  dimensions  are  covered  by  the  letter  you  give 
as  the  l)ridge  numbei-. 

After  you  have  written  the  oi'tler  out  look  it  over 
carefully  to  see  that  you  have  given  all  the  necessary 
data  and  have  given  them  correctly  and  in  a  manner  that 
will  I)e  understood.  These  ai"e  things  to  see  that  your 
oi-dei-  contains  and  which  may  often  be  inadvertently 
left  ont  : 

l\iniless  or  insert    lenses. 


THE      MECHANICS      OF      FITTING      GLASSES  57 

Drilling  of  holes. 

Size  Eye. 

P.  D. 

^Material  for  frame  or  mounting. 

Size  of  finger-piece  mounting. 

The  date. 

If  you  cultivate  the  habit  of  inspecting  your  orders 
after  they  have  been  written  to  make  sure  that  you  have 
included  the  above  points,  in  a  short  time  a  quick  glance 
over  the  order  will  reveal  any  existing  omission. 

Drilling  Holes  in  Lenses 

AVlien  specifying  for  the  drilling  of  lenses  it  is  well 
to  remember  that  the  number  of  holes  ])er  pair  is  always 
considered.  For  instance,  if  you  should  order  a  lens 
drilled  "two  holes"  it  would  be  understood  that  you 
meant  two  holes  per  pair,  one  hole  in  each  lens.  When 
no  further  instructions  are  given  it  is  implied  that  these 
holes  will  be  drilled  on  the  line.  When  it  is  desired  in 
the  case  of  eyeglasses  to  have  the  lenses  set  lower  than  on 
line  drilling  will  set  them  the  instructions  for  drilling 
should  state  drill  one-sixteenth  above  or  one-eighth  above, 
according  to  how  much  lower  you  desire  the  lenses  to  be. 
When  a  hole  is  wanted  for  a  cord  or  chain  simply  say 
"Hole  for  cord." 


58 


THE      MECHANICS      OF      FITTING      GLASSES 


Illustration   of  stnij)  ^ang-e  for  ascertaining  thick- 
ness of  lenses,  and  how  drilling  of  lenses  is  specified. 


/ 

o  ' 

t " 

w 

— 

o 

— 

^ 

< 

a 

~ 

CL, 

z^r~ 

< 

~ 

cc 

f- 

m 

~ 

0:3 

— 

en 

— 

2; 

u 

^- 

^ 

E- 

u^   1 — 1 

i_.i/> 

'h 

^ 

^h 

_  -sr 

^h 

_  w 

1 

=- 

.h 

E 

--    ,, 

_CVJ 

TT^ 



"!-' 

—  -^ 

=  S 

—  s 

^ 

—    3 

-^ 

2   Holes    Per   pair   "1    16   above   line. 


3    Holes    Per    Pair    "on    line. 


4    Holes    Per    Pair    "on    line. 


Ascertaining  the  Power  of 


L 


enses. 


There  are  two  ways  in  which  to  find  the  power  of  a 
lens,  viz.,  by  using  a  lens  measure  and  by  neutralization. 
The  lens  measure  (see  illustration)  is  about  the  size  of  a 
man's  watch  and  resembles  it  somewhat  in  general  shape. 
At  one  side  there  are  three  short  pointed  rods,  the  cen- 
ter one  being  moval)le  in  the  manner  of  a  plunger,  and  the 
other  two  stationary.     By  depressing  the  central  rod  a 
corresponding  movement  will  be  noticed  in  the  hand  that 
operates  over  the  dial.    When  all  three  rods  are  of  e(|ual 
length  the  dial  will  indicate  zero;  when  the  central  rod  is 
depressed  below  this  level  the  hand  will   indicate   plus 
powers  on  the  dial,  and  when  the  central  rod  is  allowed 
to  protrude   further  than  the   other   two   the  hand  will 
stand  over  numbers  on  the  dial  indicating  minus  powers. 
To  measure  the  power  of  a  lens  the  lens  should  be  held 
in  one  hand  and  the  lens  measure  in  the  other  with  the 
dial  in  full  view;  press  the  points  of  the  measure  against 
one  face,  rotate  the  lens   so  that  the  points  pass  over 
several  meridians  of  the  lens  and  note  whether  the  read- 
ing of  the  dial  changes  as  the  measure  is  placed  over  dif- 
ferent meridians  of  the  lens.    If  it  remains  constant  the 
surface  is  a  spherical  one ;  now  do  the  same  thing  on  the 
other  side  of  the  lens,  and  if  you  determine  both  sides  to 
])e  spherical,  algebraicly  add  the  two  readings  and  you 
have  the  power  of  the  lens.     For  instance,  suppose  one 

59 


60 


THE      MECHANICS      OF      FITTING      GLASSES 


side  of  the  lens  is  phis  '2.00  (li()i)ters  and  the  other  side 
is  niinns  1.25,  tlien  the  h'lis  is  a  phis  .75  D.  If  one  side 
should  he  plus  l.(H)  and  the  other  i)lns  1.50,  then  the  lens 
would  lia\e  the  ])ower  of  plus  2.50  1). 

Now  snppose  wlien  you  i-otate  the  lens  the  measure 
shows  a  varvino'  power  over  its  surface,  then  there  is 
indication  of  the  i)resence  of  a   cylindrical  power.     In 


Lens    MeasLire. 

reg'ulai-  (not  toric)  lenses  one  uiei-idian  of  such  a  surface 
would  indicate  zero  on  the  dial  and  the  opposite  meridian 
would  iiivc  the  power  of  the  cylinder;  the  axis  of  this 
c\  linder  would,  of  course,  he  where  the  readiny^  is  zero. 
If  the  lens  is  a  sj)hero-cy linder  one  side  will  show  the 
sphere  and  llic  other  llie  cxlindei'.  Toric  lenses  are  meas- 
ui-ed  in  llic  same  \va\\  except  Hint  in  iiieasui-iui;-  the  cvlin- 
dei-  it  must  he  i-euienihered  that  there  is  hoth  a  spherical 
and  a  cylin-lrical  power  on  one  side.     For  instance,  if  a 


THE      MECHANICS      OF      FITTIXC      GLASSES 


(il 


toric  Ions  is  i>TOun(l  on  n  pins  (i  D.  base  and  contains  a 
oylindrical  lunver  ol"  pins  l.dO  D.  this  side  will  slu.w  pins 
(/in  one  moridian  (tiic  axis  ol'  tiio  cylinder)  and  pins  7 
in  the  opposite  niei-i<lian.     In  nH'asnrini;-  the  concave  side 


Neutralizing    Device. 

of  this  lens  it  mnst  l)e  renienihered  tliat  the  spiiericai  of 
the  other  side  of  the  lens  is  pins  (i  and  the  minns  power 
of  the  eoncave  side  nnist  he  ali;-el)raicly  added  to  or 
arithmetically  dedncted  from  pins  6. 

The  process  of  nentralization  is  simply  taking  lenses 


62 


TllK      MECHAXICS      OK      FITTIXC!      GLASSES 


from  the  trial  case  an<l  placiiio-  them  over  the  lens  in 
question  nntil  when  looking-  ihn)Ui>li  the  lens  it  shows  no 
power.  The  opposite  of  the  trial  k'lises  used  for  this 
pnri)()S('  will  he  tlic  power  of  llic  lens.  In  other  words, 
to  neutralize  take  lenses  of  the  coiicsponding-  o])posite 
j)ower — plus  to  neutralize  minus  and  vice  versa.  Ke- 
meniber  when  looking  through  a  plus  lens  and  moving  it 


Stoco   Lens  Centering   and   Axis   Finding    Instrument. 

from  side  to  side  that  things  viewed  will  ai)[)ear  to  move 
opposite  to  the  direction  in  which  the  lens  is  moved,  and 
when  looking  thiough  a  minns  lens  things  will  ai)pear  to 
move  in  the  same  direction  in  which  the  lens  is  moved, 
and  that  when  the  zero  is  reached  no  movement  will  be 
discernible.  Tn  placing  cylinders  over  the  lens  the  power 
^vill  be  the  o|)posite  ol"  the  test  lens,  but  the  axis  will  be 
the  same  as  that   indicated  b\-  the  test   lens. 


THE      MECHANICS      OF      FITTINCI      GLASSES 


£3 


Tn  these  two  tests  the  lens  iiieasiu-c  if  i)i-(.perly  ad- 
justed will  l)e  reasonably  acenrate,  hnt  when  absolute  pre- 
cision is  deiuanihMl  the  process  of  neutralization  must  be 
employed.  It  will  l)e  found  advantageous  to  use  the  lens 
measure  first  and  then  the  test  lens  for  neutralizing,  as 
the  lens  measure  will  show  ai^proximate  results  and 
having  used  it  first  will  save  niucli  time  in  s<'le('ting  the- 
))r()per  lenses  for  the  neutralizing. 


A.  O.   Co.  Centering    and   Axis    Finding    Instrument. 

Having  determined  the  focal  power  of  the  lens  it  is 
alwavs  well  to  make  a  test  to  see  whether  the  lens  con- 
tains a  i)rismatic  power.  To  locate  the  presence  of  a 
prism  proceed  as  follows:  Look  thi-ough  the  lens  at  a 
vertical  straight  line  on  the  wall  or  drawn  on  a  piece  of 
paper.  Hold  the  lens  at  such  a  distance  from  this  line 
that  it  is  clearly  visil)le ;  in  cases  of  high  power  lenses  it 
will  be  necessary  to  approach  (piite  close  to  the  line. 
Hold  the  lens  so  that  its  DOtli  meridian  is  absolutely 
vertical  and  move  it  over  the  line  so  that  the  lens  is  cen- 
tered over  it  and  notice  whether  the  portion  of  the  line 


64 


THE      MECHANICS      OF      FITTINO      GLASSES 


that  is  viewed  tliroiigh  the  lens  is  a  direct  continuation  of 
the  line  viewed  outside  of  the  lens;  in  other  words,  note 
whether  there  is  a  displacement  of  the  line  to  one  side  or 
the  other  of  the  ends  of  the  line  thai  aii[»r()a('h  the  two 
sides  of  the  lens.  If  the  line  is  continiious  without  dis- 
lilacciiiciit  there  is  no  prismatic  ]h)W(M'  in  the  lens,  hnt  if 


Lloyd   Axometer. 


there  is  a  displacement  there  is  a  prism  there.  The  apex 
of  the  prism  will  be  in  the  direction  the  line  is  displaced. 
There  are  two  ways  of  measuring  the  ])Ower  of  the  prism: 
Charts  are  made  to  hang  on  the  wall  which  indicate  the 
power  of  the  prism  liy  the  amount  of  displacement  and 
there  are   nu'chanical    prism   measures   for   the   purpose. 


To  Ascertain  the  Position  of  the  Plus  and 

the  Minus  CyHnder  in  a  Compound 

Lens  by  Simple  Inspection. 

You  may  pick  up  a  lens  that  is  a  spliero-cylinder  aud 
see  that  the  cylinder  is  present  and  by  rotating  the  lens 
tell  when  you  liave  the  two  principal  axes,  but  there  are 
few  who  know  the  following  simple  truth:  When  a 
sphero-cylinder  is  rotated  on  its  optical  center  objects 
viewed  through  it  will  appear  to  move  against  the  move- 
ment of  the  lens  at  the  axis  of  a  plus  cylinder  and  with 
at  the  axis  of  a  minus  cylinder.  Thus  a  lens  of  the  power 
+  50  Sph.  +  50  Cyl.  axis  90,  will  show  an  against  move- 


Card     Protractor. 


66 


THE      MECHANICS      OF      FITTING      GLASSES 


meiit  wlieii  rotated  across  the  !)l)tli  meridian  and  a  with 
movement  when  rotated  across  the  ISOth  meridian. 
Knowing  this  will  enal)h'  you  to  (inickly  a|)proximate  the 
power  of  a  lens  and  to  know  exactly  which  is  the  principal 
meridian  when  ])lns  cylinders  are  reckoned  on  and  which 
is  the  i)rinci})al  meridian  when  minus  cylinders  are 
considered. 


Colmascope. 


THE      MECHANICS      OF      FITTING      GLASSES 


67 


Kryptoscope. 


The  Colmascope,  shown  on  Page  66,  and  the  Kryp- 
toscope on  this  page  are  instruments  used  for  detecting 
strain  and  striae  in  mounted  rimless  lenses. 


Simple  Method  of  Measur- 

ing  Prismatic  Power 

iR  a  Lens. 


It  very  often  occurs  that  a  lens  containing  a  prism  is 
bronglit  to  yon  for  dnplication  and  nnless  yon  have  some 
means  of  detecting-  the  presence  as  well  as  the  power  of 
the  prism  yon  will  dnplicate  many  lenses  incorrectly.  A 
simple  bnt  remarkal)ly  accnrate  prism  measuring  device 
may  be  made  as  follows : 

On  a  strip  of  paper  al)ont  15  inches  in  length  draw  a 
vertical  line  al)ont  fonr  inches  long  close  to  the  left  hand 
edge  of  the  paper ;  at  the  top  of  and  perpendicular  to  this 
upright  line  draw  a  horizontal  line  to  run  the  length  of 
the  paper.  Starting  one  inch  to  the  right  of  the  vertical 
line  draw  other  vertical  lines  about  two  inches  high 
upward  from  the  horizontal  line,  all  just  one  inch  apart, 
until  you  come  to  the  end  of  the  horizontal  line.  Num- 
ber the  vertical  lines  consecutively,  calling  the  first  line 
at  the  left,  which  runs  down  from  the  horizontal,  Zero, 
and  the  next  line  to  the  right,  which  runs  upward,  No.  1. 
These  figures  should  be  about  one-half  an  inch  high  and 
should  be  distinctly  made,  so  as  to  be  visible  at  a  dist- 
ance of  nine  feet.  When  tlie  chart  is  complete,  i)lace  it 
on  the  wall  and  stand  just   nine  feet  froiii  it   wlii'ii  neu- 

68 


THE      MECHANICS      OF      FITTING      GLASSES 


69 


tralizing  lenses.  Wy  holding  a  lens  np  so  tliat  the  zero 
line  runs  through  the  physical  center  of  the  lens  and 
noting  the  amount  of  displacement  as  viewed  through 
the  lens  and  observing  the  number  on  the  chart  to  which 
the  zero  line  is  displaced,  you  will  have  a  very  accurate 
indication  of  the  power  of  the  prism.  The  base  of  the 
prism  will  be  just  opposite  to  direction  of  the  displace- 
ment. The  quickest  and  easiest  way  to  understand  this 
will  be  to  construct  a  chart  and  try  the  method  suggested 
with  a  prism  from  your  trial  case. 


A    Mechanical    Prism    Measure. 


A  Method  for  Simplifying 
Transpositions. 


The  rules  we  have  for  the  transposition  of  lens  val- 
ues are  so  long  and  complicated  that  there  are  very  few 
who  memorize  them  and  it  frequently  occurs  that  just 
when  we  want  to  transpose  is  just  the  time  we  are  in  a 
hurry  or  need  to  Imow  right  away  and  cannot  recall  or 
find  the  rule  to  fit  the  case. 

To  simplify  this  and  to  show  you  how  you  can  have 
the  rule  you  want  always  at  your  finger  tips,  we  have 
evolved  a  few  simple  rules. 

First  of  all,  to  eliminate  the  constant  reference  to 
changing  signs  let  us  employ  the  algebraic  method  of 
combining  quantities,  which  is  the  same  as  the  arithmetic 
or  common  way  when  adding  plus  to  plus  or  minus  to 
minus,  but  when  combining  plus  and  minus  we  take  the 
difference  and  use  the  sign  of  the  larger  number.  For 
instance,  +3  added  to  — 2  equals  +1.  In  subtracting 
algebraically  we  always  change  the  sign  of  the  number 
subtracted  and  then  proceed  as  in  addition.  Examples: 
+3  subtracted  from  +4  is  the  same  as  — 3  added  to  +4 
which  equals  +1.  — 2  subtracted  from  — i  is  the  same 
as  +2  added  to  —4  which  equals  ^2..  — 1  sul)tracted 
from  — 3  is  tlie  same  as  +1  added  to  — 3  which  eipials  — 2. 

Bv  usinii'  this  method  we  are  able  to  I'csolvc  nil  the 


70 


THE      MECHANICS      OF      FITTING      GI-ASSES  71 

rules  for  the  transposition  of  spliero-cylindors  into  one 
simple  rule : 

To  transpose  spliero-cylinders  always  add  the  sphere 
xo  the  cylinder  (algebraically)   for  the  new  sphere,  the 
power  of  the  cylinder  remains  the  same,  but  change  its 
sign  and  use  the  opposite  axis. 
Examples : 

+3  +1  Ax  90  =  +4  —1  Ax  180 
—2  +1  Ax  90  =  —1  —1  Ax  180 
+1  —2  Ax  90  =  —1  +2  Ax  180 
It  all  simplifies  itself  when  you  remember  that  add- 
ing +1  to  — 2  equals  — 1.    By  a  thorough  understading 
of  this  basic  truth  and  remembering  to  always  add  you 
will  have  the  method  firmly  fixed  in  your  mind  and  will 
not  have  to  memorize  a  complicated  set  of  rules  or  even 
one  rule. 

In  combining  two  cylinders  we  pursue  just  the  oppo- 
site course  from  that  for  sphero-cylinders,  in  that  instead 
of  adding  we  always  subtract.  Suppose  we  have  the  two 
cylinders  +1-00  ax  180  and  -f  3.00  ax  90  which  we  wish  to 
combine  in  a  sphero-cylinder  form,  the  result  is  -f  1.00 
-f  2.00  ax  90. 

The  rule  for  combining  cylinders  is : 
Take  the  power  of  the  first  cylinder  for  the  sphere; 
subtract  (algebraically)  the  first  cylinder  from  the  sec- 
ond for  the  new  cylinder  and  use  the  same  axis  as  that  of 
the  second  original  cylinder.    Examples : 

—1  Ax  90  and  +2  Ax  180  =  —1  +3  Ax  180 
or  +2  —3  Ax  90 
Also 

—4  Ax  90  and  —2  Ax  180  =  —4  +2  Ax  180 
or  —2  —2  Ax  90 


72  THE      MECHANICS      OF      FITTING      GLASSES 

To  reduce  a  sphero-cylincler  to  two  cylinders  we  do 
just  the  reverse  of  the  a])ove.  The  rule  is :  For  the  first 
new  cylinder  add  (algebraically)  the  sphere  and  original 
cylinder  and  use  the  same  axis ;  for  the  second  new  cylin- 
der use  the  original  sphere  with  same  sign  and  an  axis 
opposite  to  that  in  the  original  compound. 
Examples : 

+1  +2  Ax  90  =  +3  Ax  90  and  +1  Ax  180 
Also: 

—2  —2  Ax  90  =  —4  Ax  90  and  —2  Ax  180 
Likewise : 

—1  +3  Ax  180  =  +2  Ax  180  and  —1  Ax  90 


Decent  ering  Lenses  for  Prism 


Val 


ues. 


The  base  upon  which  these  fonimlas  have  been  con- 
structed is  the  simple  fact  that  a  1  diopter  lens  decentered 
9.4  millimeters  will  have  a  prism  power  of  1  degree. 

Formulas : 

9.4  X  Prism 

=  Decentration. 

Lens 
Lens  X  Decentration 
=  Prism 

9.4 
From  which  we  have  the  following  rules: 
To  find  the  amount  of  decentration  (in  m.m.)  needed: 
Multiply  9.4  by  the  strength  of  the  prism  in  degrees  and 
divide  by  the  strength  of  the  lens  in  diopters. 

To  find  the  strength  of  prisut  (in  degrees)  for  a  cer- 
tain decentration:  ^lultiply  the  power  of  the  lens  in  diop- 
ters by  the  amount  of  decentration  in  millimeters  and 

divide  by  9.4. 

These  rules  apply  to  both  convex  and  concave  lenses, 
but  it  must  l)e  remembered  that  the  base  of  prism  will 
be  opposite  in  plus  and  minus  lenses.  Another  point  for 
emphasis  is  in  determining  the  amount  of  prism  or  de- 
centration in  sphero-cylindrical  lenses  the  dioptric  power 
in  the  meridian  of  decentration  is  the  value  to  be  used  in 
making  these  computations. 

73 


Estimating  the  Power  of 
Lenses  with  Calipers. 


Taking  the  glass  ordinarily  used  in  the  manufacture 
of  lenses,  it  is  possible  to  estimate  the  power  of  a  lens  by 
the  difference  in  thickness  of  the  periphery  of  the  lens 
as  compared  with  the  thickness  at  the  center.  Suppose 
the  lens  is  40  millimeters  in  diameter,  then  a  difference 
in  thickness  of  two-fifths  of  a  millimeter  means  that  the 
lens  is  one  diopter,  or  if  the  lens  is  not  so  wide  as  this  the 
proper  deductions  must  be  made  accordingly.  For  in- 
stance, suppose  the  thickness  at  the  center,  as  measured 
with  calipers,  is  2  mm.  and  the  thickness  at  a  point  10 
mm.  from  the  thickest  point  is  2  4-5  mm.,  this  would 
mean  that  the  lens  is  minus  4  D.,  for  at  10  mm.,  which  is 
the  radius  corresponding  with  a  diameter  of  20  mm.,  1-5 
mm.  difference  in  thickness  would  correspond  to  1  D.,  and 
since  the  difference  in  this  case  is  4-5  mm.,  the  lens  must 
be  4  1).,  and  since  the  center  is  thinner  than  the  periphery, 
it  must  be  a  minus  lens.  When  we  consider  the  exactness 
of  some  of  the  calipers  that  are  made,  it  is  easy  to  see 
how,  by  this  method,  a  very  close  approximation  to  the 
actual  power  of  a  lens  may  l)e  made. 


What  to  Do  (or  Loose 
Screws. 


By  loose  screws  in  this  sense  is  meant  screws  that 
require  frequent  tightening  and  which  appear  to  refuse 
to  stay  tightened. 

Screws  may  be  chronically  loose  for  several  reasons, 
principal  of  which  are  stripped  threads,  enlarged  hole  or 
a  screw  that  is  not  designed  for  the  particular  threads  of 
the  straps. 

If  the  threads  are  stripped  on  the  screw  the  remedy, 
of  course,  is  a  new  screw,  but  if  the  threads  are  stripped 
in  the  straps  another  plan  must  be  followed  which  will 
also  apply  to  cases  in  which  the  hole  has  become  some- 
what enlarged.  Provide  yourself  with  what  is  known 
as  a  repair  screw  tap  which  differs  from  the  ordinary 
screw  tap  in  that  it  is  a  trifle  thicker,  its  purpose  being 
to  make  new  threads  in  a  hole  slightly  larger  than  the 
regular  size.  Take  out  the  old  screw  and  the  lens  and 
turn  the  repair  tap  in  the  hole  until  it  projects  from  the 
other  side  of  the  straps.  Now  you  will  need  what  is  called 
a  repair  glass  screw,  a  screw  that  is  somewhat  larger 
than  the  usual  size  glass  screw.  A  supply  of  repair  glass 
screws  should  always  be  kept  on  hand  for  just  these 

cases. 

Should  you  have  a  steel  screw  that  you  can't  keep 
tight  and  cannot  duplicate,  it  can  be  tightened  once  for  all 

75 


76  THE      MECHANICS      OF      FITTING      GI  ASSES 

by  dipping  in  cyanide  of  potassium  or  anytliiiig  else  tiiat 
will  cause  rust  to  form  and  then  replacing  it  in  the 
mounting.  To  remove  such  a  screw  all  that  is  necessary 
is  after  having  removed  the  lenses  to  heat  the  part  con- 
taining the  screw  to  a  high  temperature  and  to  pack 
bees'  wax  around  this  part  and  let  it  stay  this  way  for  a 
few  minutes;  the  wax  will  melt  and  run  in  around  the 
screw  and  cut  the  rust  and  the  screw  can  be  turned  in 
the  threads  just  the  same  as  when  it  was  first  put  in. 


How  to  Mount  Rimless 
Lenses. 


The  first  requisite  in  the  successful  mounting  of 
lenses  is  to  have  the  proper  tools.  In  addition  to  a  good 
screwdriver  and  strap  bending  pliers  it  is  necessary  to 
have  a  screw  tap  and  a  rat-tail  file. 

A  screw  driver  should  be  selected  that  is  short 
enough  to  permit  the  top  of  it  to  rest  in  the  palm  of  the 
hand  and  this  top  should  be  revolving  so  as  to  allow  the 
driver  to  be  turned  without  your  losing  a  purchase  on  it. 
It  is  a  very  common  occurrence  to  see  someone  who  is 
putting  a  screw  into  a  pair  of  glasses  holding  a  screw 
driver  by  the  first  three  fingers  and  the  screw  driver 
pointing  upward  past  the  forefinger.  This  is  a  ques- 
tionable method,  for  it  is  too  easy  to  let  the  screw  driver 
slip  when  held  in  this  position  and  you  do  not  have  a  good 
hold  on  the  screw  itself.  Some  prefer  to  pick  up  and  in- 
sert screws  with  a  pair  of  tweezers,  but  while  at  times  it 
is  advantageous  to  use  tweezers  usually  after  a  little 
practice  it  is  found  surer  and  quicker  to  pick  up  and 
insert  screws  with  the  thumb  and  forefinger. 

The  secret  of  mounting  rimless  lenses  properly  lies 
in  having  the  straps  of  the  mounting  lying  flat  on  the 
lenses,  and  in  having  the  three  holes— the  one  in  the  lens 
and  the  two  in  the  straps— in  perfect  alignment  both  in 
regard  to  being  one  right  over  the  other  and  in  being 


77 


78  THE     MECHANICS      OF      FITTING      GLASSES. 

parallel  so  that  the  threads  in  the  two  straps  will  coin- 
cide with  the  threads  of  the  screw. 

Tlie  first  step  is  to  arrange  the  straps  so  that  they 
will  lie  flatly  on  the  lens  and  so  that  the  distance  between 
them  will  correspond  to  the  thickness  of  the  lens.  To 
accomplish  this  it  is  necessary  in  most  cases  to  bend  the 
straps  slightly  closer  together  or  farther  apart.  This 
bending  of  the  straps  can  be  done  with  ordinary  snipe- 
nose  pliers  but  it  is  best  to  use  strap  pliers  that  are 
especially  designed  for  this  purpose,  for  by  using  these 


strap   Pliers. 


special  pliers  the  bending  and  paralleling  of  the  straps 
can  be  done  all  at  the  same  time  without  likelihood  of 
breaking  the  straps. 

Having  the  straps  properly  bent,  the  next  step  is 
to  insert  the  lens  between  them  and  to  try  the  holes 
through  the  straps  and  lens  with  a  screw  tap  to  make 
sure  that  all  three  holes  are  in  line  and  the  threads  on 
the  straps  will  take  the  screw  without  forcing.  In  trying 
the  threads  with  the  screw  tap  turn  the  tap  a  few  times 
in  the  hole  (with  the  lens  in  the  straps)  until  the  end  of 
the  screw  tap  projects  slightly  through  the  other  side  like 
a  screw  would  do.    If  you  find  the  tap  turns  without  re- 


THE      MECHANICS      OF      FITTING      GLASSES.  79 

quiring  much  force  or  without  binding,  you  may  insert 
the  screw  and  turn  it  down,  but  if  the  tap  binds  in  the 
threads  it  indicates  either  that  the  sides  of  the  straps  are 
not  parallel  or  else  the  hole  in  the  lens  does  not  center 
properly  over  the  holes  in  the  straps  or  perhaps  both  con- 
ditions exist.  If  the  hole  in  the  lens  does  not  line  up 
properly  with  the  holes  in  the  straps,  ascertain  by  in- 
spection where  the  lens  hole  binds  on  the  screw  tap  and 
which  way  the  lens  needs  to  be  moved  or  the  hole  needs 
to  be  enlarged  so  as  to  admit  the  screw  without  pressing 
against  the  glass.  Often  it  will  be  found  possible  to  move 
the  lens  in  the  proper  direction  by  bending  the  edge 
straps  down,  on  the  lens  or  away  from  it.  By  "edge 
straps"  is  meant  the  upright  straps  that  press  against 
the  edges  of  the  lenses.  These  edge  straps  should  be 
bent  so  that  they  lay  firmly  against  the  edge  of  the  lens, 
following  its  contour  as  closely  as  possible.  If  it  is  not 
found  possible  to  line  up  the  hole  in  the  lens  by  moving 
the  entire  lens  and  adjusting  the  straps  then  the  hole 
must  be  enlarged  at  the  place  where  it  binds  on  the 
screw,  but  this  should  be  the  last  resort  as  a  hole  that 
is  larger  than  necessary  will  cause  the  lens  to  loosen 
easily  and  to  require  frequent  tightening  of  the  screw. 

To  enlarge  the  hole  use  a  round  rat-tail  file.  Moisten 
the  file  slightly  and  having  inserted  it  in  the  hole  file 
against  the  glass  where  the  screw  binds.  Usually  a  little 
filing  will  suffice  and  it  is  better  to  make  the  screw  tap 
test  after  one  or  two  strokes  of  the  file  than  run  the  risk 
of  filing  away  too  much  glass. 

When  the  holes  are  properly  aligned  and  the  straps 
correctly  adjusted  insert  the  screw  and  turn  it  down 
firmly  but  if  you  find  it  binds  even  a  trifle  take  the  lens 


80  THE      MECHANICS      OF      FITTING      GLASSES 

out  aud  endeavor  to  discover  the  cause,  for  while  you 
may  be  successful  in  g-etting  the  screw  all  the  way  in 
without  breaking  the  lens  if  it  binds  at  any  point  the 
lens  will  crack  "all  by  itself"  as  your  patients  will  tell 
you,  within  a  few  hours  or  perhaps  a  day  or  so  after  you 
mounted  it. 

The  proper  way  to  hold  a  mounting  and  the  lens  you 
are  setting  up  is  to  place  your  forefinger  under  the  strap 
and  lens  and  your  thumb  on  top  of  the  mounting,  in  other 
words,  hold  the  mounting  in  your  hand  with  your  finger 
right  under  the  strap  that  the  screw  last  goes  through 
and  if  the  straps  are  properly  bent  the  combined  pressure 
of  the  straps  and  your  finger  will  be  sufficient  to  hold  the 
lens  in  position. 

After  the  screw  is  in  place  the  pointed  end  should  be 
cut  oft'  with  cutting  pliers  close  to  the  strap.  If  end-cut- 
ting i^liers  are  used  you  will  usually  get  a  clean  cut,  but 
if  you  use  side-cutting  pliers  it  will  be  necessary  to 
smooth  oft"  the  end  of  the  screw  with  a  fine  flat  file,  and 
in  doing  this  care  must  be  exercised  not  to  file  away  the 
surface  of  the  straps,  for  if  the  latter  is  gold  filled  filing 
its  surface  will  expose  the  base  metal  and  that  portion  of 
the  strap  will  be  likely  to  corrode. 

In  summing  up  the  mounting  of  rimless  lenses  just 
one  point  must  be  emphasized:  It  is  not  hard  if  you 
reason  it  out  and  above  all  things  do  not  force  a  screw, 
remembering  that  if  yon  have  to  force  it  there  is  indica- 
tion that  it  binds  somewhere,  most  probably  against  the 
glass  and  the  lens  will  break  at  the  first  jar  and  you  will 
have  what  is  known  as  a  "screw-crack"  or  a  lens  that 
broke  mysteriously. 


Record  Systems  (or  the 
Refractionist. 


One  of  the  most  important  departments  in  the  busi- 
ness of  the  refractionist  is  the  records,  and  it  will  be  well 
worth  the  time  required  to  study  into  this  matter. 

In  the  first  i3lace,  the  records  must  be  in  such  shape 
that  they  will  offer  the  greatest  convenience  and  sim- 
plicity when  it  is  found  necessary  to  consult  them.  In 
installing  a  record  system  this  is  one  of  the  very  first 
things  to  be  considered,  because  the  reason  you  keep 
records  is  that  you  want  the  information  for  future  refer- 
ence and  you  want  to  obtain  it  accurately  and  quickly. 

There  are  two  general  forms  of  record  keeping ;  one 
is  the  book  in  which  the  leaves  are  permanently  bound, 
and  the  other  is  the  loose-leaf  or  card-index  system. 
Both  of  these  have  their  respective  advantages  and  dis- 
advantages. The  bound  book  is  secure  and  pages  cannot 
be  lost  out  of  it  without  l^eing  torn  out ;  at  the  same  time 
it  is  rather  bulky  and  much  space  must  be  kept  idle  for 
considerable  time  if  it  is  desired  to  keep  the  full  history 
of  a  case  together  and  when  the  full  history  cannot  be 
kept  together  conditions  become  complicated  and  there  is 
likelihood  of  error  or  else  much  additional  work  in  mak- 
ing notations  on  every  record,  necessitating  a  long  search 
when  a  case  is  to  be  traced.     The  only  objection  to  the 

81 


82  THE     MECHANICS     OF     FITTING     GLASSES 

card  system,  is  that  cards  may  be  mislaid  or  lost,  but  this 
ditficulty  can  be  easily  overcome. 

The  writer  is  very  decidedly  of  the  opinion  that  the 
loose-leaf  or  card  index  systems  are  the  most  satisfactory 
and  efficient.  Some  find  it  convenient  to  combine  the 
loose-leaf  and  card-index  systems,  by  using  light  weight 
cards  in  a  loose-leaf  binder  and  when  these  records  are  no 
longer  needed  for  immediate  reference  to  remove  such 
cards  and  place  them  in  a  filing  cabinet  or  drawer  espe- 
cially made  for  the  purpose.  Others  find  it  more  con- 
venient to  use  loose  cards  and  when  the  record  is  com- 
plete, and  the  prescription  has  been  transferred  to  an 
order  blank  for  transmission  to  the  manufacturing  opti- 
cian, the  record  card  is  placed  in  the  filing  cabinet  at  once. 
This  is  simply  a  matter  of  detail  and  can  be  arranged 
to  your  own  preference  without  materially  affecting  the 
system  in  general  as  recommended  in  this  article. 

Cards  for  this  purpose,  already  printed,  may  be 
bought,  but  in  the  long  run  it  may  prove  more  economical 
to  have  the  cards  especially  printed  to  meet  A'our  own 
particular  requirements.  Every  man  has  different  ideas 
in  regard  to  what  he  wants  recorded  and  it  is  these  little 
details  that  make  the  stock  printed  cards  unsatisfactory. 
There  are  certain  things,  however,  that  all  cards  must 
show,  and  they  are  as  follows : 

The  patient's  name,  address  and  age. 

The  date  (this  is  of  utmost  importance). 

The  formula  for  the  lenses  prescribed  to  be  worn 
(both  the  distance  and  near  correction  should  be  given). 

The  frame  nicasurements. 

The  kind  of  glasses  supplied  on  the  original  order 
and  the  price. 


THE     MECHANICS     OP     FITTING     GLASSES 


83 


The  following-  infoniiation  will  prove  of  value: 

The  patient's  complaint  when  coming  to  yon  for 
treatment  or  glasses  and  a  description  of  any  peculiari- 
ties not  shown  by  the  refraction  record. 

The  patient's  occupation. 

The  formula  of  the  lenses  previously  worn. 

The  result  of  the  retinoscopic  test. 

The  patient's  full  correction  (this  often  will  differ 
from  what  you  prescril:)e  to  l)e  worn). 

The  condition  of  the  extrinsic  muscles. 

Did  the  patient  come  to  you  through  an  advertise- 
ment, or  recommendation  of  a  friend — if  so,  the  name  of 
same. 

Having  completed  such  a  record,  should  the  patient 
return  at  some  later  date  and  you  find  the  condition  of 
the  eyes  to  be  different,  a  new  card  should  be  made  out 


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and  attached  to  the  front  of  the  old  card,  and  a  notation 
should  l)e  made  on  the  old  card  showing  that  a  new  pre- 
scription has  been  written. 

A  portion  of  the  card,  usually  on  the  reverse  side 
should  be  reserved  for  a  record  of  l)usiness  transactions 


84  THE     MECHANICS     OF     FITTING     GLASSES 

with  tlio  ])ati(Mit.  For  instance,  suppose  ^Ir.  Lynn  i\ 
Doyle  slumld  jnociire  a  pair  of  glasses  from  you  on  Jan- 
uary loth  and  on  May  1st  he  breaks  a  lens  in  the  glasses 
he  uses  for  distant  vision,  and  come  to  you  to  have  it  re- 
placed. You  have  classified  and  indexed  the  drawer  that 
contains  the  cards  so  that  all  you  have  to  do  is  to  look 
under  the  Letter  D  and  find  Mr.  Doyle's  card.  This  will 
show  exactly  what  his  lenses  should  he  and  all  doubt  in 
this  regard  is  eliminated.  Here  is  where  the  extra  space 
will  be  of  use:  enter  here  something  like  this:  "May  1, 
1915,  one  right  lens  (D.  V.),  $2.00."  The  next  time  he 
comes  in  for  a  rei)air,  or  to  have  a  lens  replaced,  make  an 
entry  on  the  card  showing  the  date,  what  he  got  and  what 
the  price  was.  This  method  will  be  of  value  in  two  ways; 
it  will  obviate  the  possil)ility  of  doubt  or  controversy  re- 
garding the  price  and  >ou  will  have  a  detailed  record  of 
just  how  much  business  he  does  with  you  and  at  any  time 
you  can  run  through  your  cards  and  ascertain  just  how 
much  business  you  have  done  during  a  specified  period. 
It  will  also  prove  advantageous  where  there  are  niore 
persons  than  one  in  your  office  to  use  the  records. 


INDEX 


Page. 

Adjusting  eyeglasses 40 

Adjusting  spectacles   37 

Angle  of  l)ridge 28 

Axis  finders  <J2,  (J3,  G4 

Axis,    locating   in    cylinders 60,  65 

Base   of   bridge 23,28 

Bifocals — 

Defined    16 

Fitting  frames  with 36 

Kinds 17 

Bridge,  eyeglass  14 

Bridge,  spectacle — 

Adjustment  of    37 

Angle  of   28 

Base  of 23,  28 

Crest  of   23,  27 

Height   of    23,  27 

Table  of  sizes  of 23 

Cards,  measuring 25 

Cement  bifocals   17 

Centering  machines 62.  G3,  64 

Charts,  prism    68 

Combination  mountings 14 

Crest  of  bridge 27,  28 

Crest  measures 29 

Cylinders,   locating  axis  of 60,  65 

Decentration    for    prisms 73 

Definitions   9 

Drilling   holes   in   lenses 32,  57,  58 

End-pieces,    angling    of 39 

End-pieces,  defined    11 

Eyeglasses — 

Adjustment  of 40 

Finger-piece 14,  32,  47 

Fitting  sets  of 32 

Fitting  of 20,  29 

Measuring  for 20,  29 

Parts  defined    9,  11 

Finger-piece  eyeglasses 30,  47 

Fitting  sets,  eyeglasses 32 

Fitting  sets,  spectacles 26 

Frames,   adjustment  of 37 

Frames,    definition    of 9 

Gauges,  strap 58 

Grab  backs 14 

Grab  fronts   14 

Guards,  eyeglass — 

Adjusting 40 

Illustrations  of 12 

Selection  of   32 

Holes,   drilling   of 32,  57,  58 

Inspection  of  lenses — 

For  cylinders    59 

For  prisms   63,  68 


Kvypiok  lenses  17 

l^enses — 

Drilling  lioles  in 32.  57,  58 

How  to  mount 77 

Measures 59 

Neutralizing   59,  61 

Sliapes  of 19 

Size    to    prescribe 31.  32,  33 

Sizes  explained   18,  24,  31.  33 

Sizes,   table  of 18 

Transposition  of 70 

Lentieulars 18 

Measures — 

Cards 25 

Crest    29 

Lens  60 

Prism 69 

Meniscus  lenses   16 

Neutralizing  lenses    59,  61 

Nose,  measuring  the 27 

Opifex  bifocals   17 

Perfection  bifoqals 17 

Pliers,   illustrations  of 45,46 

Prescriptions,  writing  of 49 

Prisms — 

Chart   for    68 

Decentering  for 73 

Detection  of   63,  68 

Formulas    73 

Measures  68 

Pupillary  distance — 

Of  the  eyes 21 

Of  glasses 25 

Record  systems .  81 

Screw-drivers 77 

Screws,  tightening  of .•. .- 75 

Shanks   of   bridges , 10 

Specalettes 14 

Spectacles — 

Adjusting   37 

Bridges   23 

Definitions   9 

Fitting  of   20.  26 

Measuring 25 

Springs,  eyeglass    11.  14,  32,  42 

Strap  gauge 58 

Straps   10 

Studs,  eyeglass  12,  13.  31 

Taps,  screw 77 

Temples — 

Defined    9 

Kinds  of  9 

Length  of 24.  29 

Toric  lens'-^s  16 

Tianspositions    70 

Unit  of  measure 20 

Width  of  base 23.  28 

Width,  pupillary  21 .  25 


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